try jobes tomato stakes

Stop using the fish emulsion and use any pelleted fertilizer meant for vegetables.

i also hear the dynamite pelets work great too

I have the same problem with my doberman and especially the pspillon. I want to use my free horse manure and the pap puppy keeps dragging it in the house. I can imagine beagles are awful with their great noses! We hunt jackrabbits on horseback with a beagle pack (like traditional foxhunting) here in Phoenix. Awesome little dogs. We also have a hound pack in Flagstaff and visit a harrier pack in CA.
Anyway, I've only found fencing, especially a low electric fence to be effective. My doberman I was able to use a shock collar on a low setting. I only did it once but she's very, very sensitive. I haven't done it with the papillon, mainly because the collar is too heavy but also because she's much harder head than the Doberman so that I think she would simply learn not to pick up horse poop when the collate is on. The Doberman learned "mommy doesn't like me to pick up horse poop and made my neck buzz" which would be the more desirable response.
My experience with hunting dogs is they have tunnel vision so if the collar is not on it's not going to work. The Doberman and some other working breeds are much different than hunting/hound breeds. Less tunnel vision and prey focus, more please my mommy focus. I haven't had my papillon puppy long enough to figure her out, she seems more along the lines of a border collie or spaniel, highly OCD and focused, off the charts smart but pretty independent as well.
Anyway, with beagles, your best option would be a 4-6 inch high electric fence which you can make using 1/2 inch PVC pipe for your pole, drill holes to run wire through, no worries about needing insulator for this. Add two long pieces of rebar pounded into the grounded 3-4 feet deep, 3-4 feet apart. These are your grounds. For your charges, if you have acess to electricity you can use a cheap 110 charger. If not, I would highly recommend a solar charger which works fantastically.
Make sure your grounds are kept damp as dry ground won't do as well. I water the ground poles every week if it doesn't rain.
This type of system is very effective and not ugly system

Thanks all for the follow-up and suggestions... I had tried the fish emulsion liquid as well as Kellogg's "Natural and Organic Tomato, Vegetable, and Herb" granules - and both got the dogs digging...

Well... I purchased the Jobe's "Tomato Outdoor Fertilizer Food Spikes" from Amazon... and whala... no digging from the Beagles... they're not even interested in sniffing around the tomato plants.

Thanks so much for the suggestion on the Jobes tomato spikes... I think they're going to work out great.