cayenne pepper in their holes and buy them new toys & take more walks.
I am told they’re bored when they dig, but I swear my Belgian Malinois was a truffle hunter, lol.
Train them! Digging is an instinct. Chances are they are bored and not getting enough exercise. Here are some things you can try.
I was a vet tech for 22 yrs also did training. One of the most humane but funny ways is... depending the size of your dog will decide the size of plastic container you use, for lg dogs use a gallon milk jug for med use a half gallon smaller ones use your pints or quarts but you will half to put holes in them. Take their collar and slide it through the handle then put it on the dog hanging in the front on their chest. When they dig it acts like a punching bag and catches them under their jaw. That’s the funny part they will stop and look around after a few times they will stop digging. Also give them a cool place I take gallon bags put water in them and lay them flat freeze them then put them under their blankets or beds and they have a cool area to lay if heat is the reason for their digging
Put a small fence , about 3 feet high , around your garden. Put a little gate
so you can get in and out.
Your home store ( Lowe's , Howe Depot ) will have
everything you will need. A nice little fence will look nice around the garden.