I sympathize as I'm having the same problem -- with my own cats! They think that the mulch I've put around the roses makes a great litter pan. All those supposed repellant sprays (and citrus peels -- I tried them too) might as well be water. I was searching for a product I thought I remembered that was a plastic grid in a mat with little plastic spikes sticking up (not really sharp, just enough to be unpleasant to walk on) that was supposed to keep cats out of an area because they won't walk on top of it. I didn't find that but came across this new device for sale though: cat stop . I use a similar device indoors with great success, but I don't know how well this outdoor one works as it only uses sound to scare the cats away.
The indoor version, called Ssscat, shoots a jet of harmless gas which scares the beejezus out of the cats -- the first time each of my cats encountered it they must have jumped five feet up and ten feet back, arched up, dancing on toe tips, and oh, the hurt looks coming my way. Here was this horrific hissing bottle and what was mommy doing? Half falling off her chair laughing!
I haven't tried this new outdoor type yet, but unless that ultrasonic tome is really loud, I can't see it intimidating my cats. I just bought one though, so I guess we'll see.
PS - Have you tried finding out who owns these cats? I know if someone told me my cats were digging up their yard I would try to find a solution (and pay for it as well).

You might try putting a little kitty litter box outside? I do this for my own cat but we don't have many around here. If the box can be near other matter such as leaves, dead grass, etc., I've found mine likes to mix that into her litter. (This also keeps her from using the gardens.) The first time I saw her in my garden bed (she previously had avoided them), I watered that garden after nagging persistently. She hasn't returned but who knows why cats do or don't do what they do.

Indoors, a spray product called "Cat Away" worked well in keeping her away from something or from clawing the furniture. The best defense for my cat is to nip the behavior in the bud, it seems. But they are all so different.

I'll be watching this thread for any other advice though...good luck!

Cat Deterrents for your Garden:

Keep in mind that each cat is different (like people), what works for one may not necessarily work for another. On the plus side, most cats will keep pesty squirrels, moles and other critters out of your garden. They're great for keeping out moles, rabbits, squirrels, and other critters which can do more damage in your garden than a cat ever will. Birds aren't stupid, they watch for cats and stay away. Sometimes natural law comes into play and the quicker animal wins, it's natural law.

If the cats have owners, talk to them without being confrontational. The cat owner who allows his cat to damage other peoples' property is as guilty as the cat hater who kills the cat for trespassing. Remember, cats will be cats, and it is unfair of us to blame them for being what they are and how nature intended them to participate in this world. After-all, we praise them when they catch mice or rats or other creatures we deem to be 'pests'.

* amonia soaked (corncobs, etc)
* aluminum foil
* bamboo skewers
* black pepper
* blood meal fertilizer
* bramble cuttings
* Carefresh - "recycled" wood pulp
* catnip - donated into your neighbor's yards (so they'll stay in their own yards)
* cedar compost
* chicken wire (metal or plastic)
* cinnamon
* citrus peels
* citrus spray
* cocoa bean shells
* coffee grounds -fresh & unbrewed, not just a light sprinkling (highly recommended by MANY Gardenwebbers!)
* dogs
* electric fence for animals
* essence of orange. essence of lemon, lime (citrus essential oils)
* fresh manure(ditto)
* garlic cloves
* gumballs from the Sweet Gum Tree
* gutter covers
* hardware cloth
* heavy bark mulch
* holly leaves
* keep the area damp, they like dry soil
* lavender
* liquid manure (good for your garden too)
* motion sensor sprinkler
* pennyroyal
* pinecones
* pipe tobacco
* plastic forks
* predator urine
* red wine vinegar
* river rocks over the exposed soil
* rocks, crushed
* rose bush clippings
* rue, an herb (Ruta graveolens) (highly recommended in plant form only)
* short twigs throughout the planted area about 6" apart
* six-inch bamboo skewers (pointy side up)
* Spray on your leaves (not the cat): fill a spray bottle with 1/2 t chili powder, 1/2 t cayenne pepper, 1 t dish soap and water
* squirt gun with water
* talk to your neighbors
* tansy
* thorny berry, lilac, hawthorn, rose clippings
* toothpicks
* upside down vinyl carpet
* vinegar sprayed on areas where they roam
* water bottle on "stream"

NOT RECOMMENDED:
*** chili powder, red crushed pepper, cayenne pepper (NOT recommended), it gets on the cat's paws then they wash themselves and they get it in their eyes, beware cats have literally scratched their eyes out because of this. Even if it's one cat out of 500 infected in this way, that's one too many for me.
*** Don't ever use mothballs or flakes. Those little toxic waste pellets destroy cats' kidney function, could seriously harm people who handle them, and yes, contaminate your own garden soil. Their packaging even warns against using them this way.

Give them their own areas:

(To keep them out of where you don't want them)
(If you don't mind them protecting your garden from other critters)

+ pick the cat up and bring it to eye level with the plant to see and smell it up close. She noted that once her cat has seen and sniffed at the plant, she usually doesn't bother with it later.

+ give them their own plants - i.e., pots of grass for her to chew on and a place in a large planted container on her balcony with some miscanthus grass in it (the cat likes to curl up in that for some reason)

+ if the cats are strictly indoors and attracted to your houseplants, grow catgrass for them. If someone forced you to remain inside one enclosed structure all your life, you might be attracted to the plants too.

+ Barley Grass
+ Any type of "catgrass" from the pet store
+ Carex elata 'Bolwes Golden' but put it in some shade
+ Catmint Nepeta mussinicultivars (Simply put, Catmints are Catnips without any culinary or feline use. In any case, they are, however, phenomenal, long flowering, hardy perennials that belong in every fairie or flower garden.)
+ Catnip Nepeta cataria (in your own yard) The oils of which also work as a mosquito repellent that works 10 times better than Deet! Catmint is the common name for all varieties of Nepeta. Catnip is the common name for the specific variety of Nepeta called nepeta cataria, which is the variety that cats are most attracted to.
+ Cat Thyme (Teucrium marum)
+ Flax
+ Oat Grass
+ Jacob's Ladder
+ Lemon Grass
+ Loose soil and mulch like small bark mulch
+ Mints
+ Purple Fountain Grass so the cat lays in the long leaves all day. Maybe put something in that the cats really like and - you know cats won't winky were they like to hang out.
+ Sandy area
+ Silver vine (Actinidia polygama)
+ Striped Ribbon Grass (can be invasive)
+ Sweet grass
+ Trificum aestivum (type of cat grass)
+ Various Varieties of Cat Mints (Catnips)
+ Wheat Grass
+ Wheat Berries
+ Valerian

This list compiled by Violet_Z6, email at violetgw@care2.com for comments and suggestions regarding this list.

Well, I tried the cat stop ultrasonic repellent and it didn't work. I don't know if I got a defective unit though because the little red light blinked once and then never blinked again.
I did put a litter pan on top of where they were going for awhile and they went in it when I had it out. I eventually took it away though because it was right by our front gate... not too pretty having people walk in and the first thing they see is a big litter pan sitting in the rose bed.
I think my next thing to try is to find a discrete place for an outdoor litter pan (so as to give them an outdoor place to go) and try those mats with the little prickly plastic spikes.

I have the stray cat problem in my back yard. I am tired of digging up the poop that they bury all over the place. Am a little concerned at the possibility of bacteria/disease too. All those home remedies and mixtures are a waste of time and money. They only work temporarily. I even managed to spray the cats with water , but they keep coming back. It is always the same three cat suspects. I won't bother with the cat alarm sirens because they are too expensive and the siren doesn't blare long enough to make a lasting impression on the cats

Why are people saying that cayenne causes cats to scratch their eyes out. I saw a couple city government web pages that recommended cayenne. I don't think they would endorse anything that would injure the felines. I once used a mixture of cayenne, mustard, vinegar, and habanero pepper. But again, it only works for awhile and the cats will find another place where you didn't apply the mixture. Besides cayenne is too expensive. I didn't see any cats wearing eye patches afterwards.

I have another idea. My back yard is ringed by a high cinderblock wall. What about coating the top of this entire wall with a long lasting non-toxic sticky substance? I hear cats hate stepping into anything sticky.

Any opinions on this?

Thanks,
Dave

Ugh I have the same problem with cats. My neighbor keeps approximately 7 feral cats and their mother and father mostly outdoors. Even in a foot of snow those cats are outside, climbing down my fence and pooping in my flower beds.
This is a serious problem with me since I'm pregnant and not that far along. And when the weather warms it still won't be advisable for me to plant anything there with my (ha, ha) condition. My doctor says to wear gloves and a mask, but frankly the smell is so bad I can't go near that particular bed!
I need some advice on a prickly shade-loving vine for that area that they intrude. I'm planning on cutting some of my older roses just for the prickly thorny stems to lay in the bed, but I want something long-term as well.
I only just moved into this house last summer (colorado springs area) so I'm not comfortable talking to my neighbor. Sounds dumb, but what will he tell me? He'll probably say he has to let them out to kill the mice that try and live in his outdoor dove cage.
And worstly, the fence that separates us is actually a 5 foot wall of stones on my side(meaning my yard is 5 feet shorter than his), with about a foot and a half between his and my fence (leaves and sticks get lodged between my fence and the wall of rocks)...so anything that I plant will either be on HIS turf, or 5 feet below on mine, needing to be trained up up up to cover our fence!
And of course I'd like it to grow in quickly! I think I'm asking too much here--this would be like a miracle plant lol.
I've tried all the natural remedies like cinnamon, etc, but these cats just drop in and out to poop so quickly they don't seem to notice.
I've taken to raking up all the poop on nice days and just throwing it back over to his side ROTFL! But the smell is unbelievable! I have two cats, but they aren't supposed to be outside. Sometimes they sneak out of course!
I wish my garden hose was closer to this side of the house--I'd squirt them every night!
I don't know...does anyone think it'd be cowardly to post a note on his door asking him to provide his mangey cats with an outdoor litter box? lol. I get all pipsqueaky around strangers! It's either that or waiting to find and grow this vine that I imagine would work.....

I used a rather unorthodox approach. My neighbor's male cat was using one particular flower bed for his litter box. I put a boogie bass where he was going. As soon as he started digging, it would activate the boogie bass and scare the crap out of him. Very entertaining for me and it worked after only two attempts on his part. I've seen no evidence of him in over 6 months. I was thinking of getting the dancing lobster if he comes back.

Those darned cat are driving me nuts. And the owner drives off and doesn't have a clue. I have tried all the usual anti-cat methods and the cats only laugh at me.
They poop away in my flower bed - reeks to high heaven. My bird population is on the decline. And that is the part that really frosts my patooty!

I really want to give the cats a one way ride to another domain....

Use rock, bark, wood chip or living ground cover plants as mulch.

Put chicken wire or bird netting over the soil where ground covers haven't grown in yet.

Fishock electric fences are available at Petco, Petsmart and many feedstores. They are lower voltage than livestock fences and easy to install. Many use them to protect ponds from raccoons.

The site below has directions for a do it yourself motion activated sprinkler. Click on Predators. The commercial brand name is "Scarecrow". You can buy them for about fifty bucks at many garden/pond stores. Works on deer too.

My sympathy to the folks whose neighbors' cats are using their yards as a litter pan. In our case it is our own, who have decided the hosta bed under the family room windows is a dandy toilet.
Bought deer-keep-out mesh from Gempler's,to cut to size of bed, pin down with stakes & deter them. However, cats & other animals return to the same spot to poop---it marks their territory to others---the thing that has worked (this year, so far) is watering the bed so much & so often it is no fun to dig in. Too wet. Also removed poops & put in plastic bag then trash.
When neighbor's dog was allowed to use our yard as potty, we just kept throwing the prizes onto her driveway. Eventually she got the message. The owner, not the dog.
I would also squirt the cats with the hose--others' cats, not my own.It won't hurt them & it certainly gives them the message they are not welcome in your yard. It's a territory thing--they are pooping in your yard because it is in their territory, or on a boundary between them & some other cat---sometimes these line up with "our" boundaries, and sometimes they do not. Cats establish & keep their territories by making intruders wish they hadn't--you can do it, too.