I like the idea of the paint balls sending a message to both dog and owner, but you've got to purchase the gear and catch the dog on your property. As good of an idea as this is, it's a huge waste of valuable hunting time and money.
I would handle it one of two ways:
#1 Legal: Notify the owner (very politely) of the problem and your legal course of action.
#2 The SSS Rule.
The bad thing about the above 2 ways of handling it is that you have to choose one or the other and stick with it. You can not choose method #1 and switch to method #2 and certainly not the other way around. If you know that the legal method is going to work, then that's the course of action I'd take. If not, method #2 works like a charm.
Bowhunter57