a high powered paint ball gun gets the message across to both dog and owner. Won't kill the dog but puts a nasty whelp and a lovely splat of bright colored paint. Hurts like a bugger for the dog and the neighbor knows he's been shot and worries that next time it won't be paint and will find a way of keeping the dog home. Sends a clear message that you can and will but would prefer not to kill their dog. Done it many times with good results!
