Move.
I had a co-worker who had a common yard with his sister. The brother-in-law held a grudge because of some sidebar comment that had been made twenty years prior. As a result, the dog was trained to crap on my co-workers patio. The rest of their relationship was perfectly functional. When the little niece told him that the dog was trained to do that, my co-worker decided to move rather than start a family feud. Enter housing collapse, and I think he now owns two houses that he cannot afford.