dog...
Man, I hate dogs. Don't look at them (you know that right?).
I think that I would call the cops, and possibly talk to an attorney about the situation. If you don't get a positive response from either of those outs, I would invest in some rat poisoning and a pound of hamburger meat. Then go by this jerks house one night after he goes to bed and toss the doggy treat out in the yard. That'll do the trick...
I know this is cruelty to animals... blah blah blah, but have you ever had rabies shots? You don't know what pain is until you have shots for rabies. I feel sorry for ya, man. I hope that you can get this taken care of.
You might want to look into your city's laws about how short a least must be to be classified as following the leash law. In my area, the leash has to be 3 meters or less (pretty good size, but not long enough for the flea bag to be able to reach a sidewalk from the frontdoor of a house). If the leash he is using is longer then what the city allows, then I believe you are justified in using pepper spray, mace, taser, ammonia, baseball bat, dog whistle, etc on the mutt and / or owner.
Let us know what happens.