Paintball guns work. Unless the dog is retarded, I've shot a few with paintball guns that have come back still covered in exploded paintballs. I also live on a farm with cattle. I've shot a few dogs that get in with the cows and get them riled up to the point that one time they trample part of my fence. Needless to say, that dog got a .243 to the head. If the owners think that they can let their dog run free since they now live in BFE, and now that you've warned them and your sheriff friend has explained the leash laws...I agree with the other posts, paintball, adoption, take it for a long drive, or kill it.