Honestly the best thing that I can think of is to get a wide angle security camera that can cover the area from your home. Then like others have said, call the authorities every time that you see the dogs cross the line. Then when the officer shows up, review the footage and give him a copy if he wants it. Then he can issue the citation. Hurt him financially, that is the best way to get to someone. Then if you are outside and those dogs make a run at you, given their history I would not hesitate to put them down. There is nothing illegal about it if they are a threat to you, or your property on your property. But if you go that rout I would recommend keeping a close eye on your pets because retaliation from the neighbor could be a real concern.

Also I heard little bowls of antifreeze are supposed to enhance the operation of a buried electric fence against dogs who no longer have a collar.