Dude, you've got to follow that motherfucker to the store where he is not on his own property, stop him in the parking lot and tell him straight up that you are a member of the MMA Community, and if he continues with these shenanigans over the dog there will be retribution............then show him a picture of his kids playing out front of his house and tell him you know where he lives. Even though you are clearly in conflict with him from right next door, this will unnerve him! There will be a for sale sign up within a week!
Also, I didn't see anywhere indicating what kind of dog it is. Please tell me this is a kind hearted, misunderstood game pit?