Make a hot pepper tea as if you were making sun tea:
put water in a gallon jug, shred/chop/puree & add the hottest peppers you can find (cayenne is good), & set the jug in the sun.

If it's too late in the year for sun tea, boil some water & toss in the peppers; turn off the heat & allow to cool.

Spritz over the areas where the dog is digging.

You'll have to refresh the pepper as it wears off, & you'll need to refrigerate any leftover "tea".

Do not use ammonia;
although it repells them from digging, it smells like tee-tee & they'll "mark" right on it!

Best luck!

Pepper did not work for me. I found the only thing that works is to scoop up some of my dog's pooh and dump it in the flowerbed. She won't touch the flowerbed now! It's nasty but effective.

I purchased some short (~18") decorative fencing from the garden supply store and put around my beds. Keeps my dogs out.