Hey Bubby,
I will bet that where you live there is an ordinance that if a dog it off his property he must be leashed. If your neighbors say it isn't their dog the only thing you can do is catch them with a camera. If you KNOW it's your neighbors dogs just notify your local animal control and tell them that you KNOW it's their dogs and that you've seen them doing the harm. Then ask them what the next step is?
Here, and I bet also where you are, you can borrow animal traps from your local animal control. Borrow a couple and see just what you get? It will cost your neighbors a few dollars to go down and get their dogs back.
If they are digging your garden up, pepper and also animal blood might work. You can get the blood from any farm supply and all you have to do is sprinkle it around the edge of the garden. If it rains, you'll have to do it all over again though.
I never thought of Paint Ball Guns but it sounds like a great idea if you have access to one.
Let your neighbors try to explain the paint all over their dogs the next day.:lol:
Good luck my friend.. I wish I could be more help and if this old mind comes up with anything else I'll be sure to let you know.
Uncle Billy