This is a cool neighbor (my current one where the dog used to bark
) My last cat Lucky would piss in his kid's sandbox. He told me about it.
But what could I do. Lucky was an outdoor cat for 10 years prev. Plus he had 8 years seniority over the neighbor and earned the right to run outdoors and always ran in that yard as the prev neighbor loved him.
I even tried an outdoor litterbox. Which he seen I was making an effort.
One day he builds a fence around the sandbox which also allowed a roof over the sandbox. Two birds.. Cool guy and totally won my respect. Money takes care of everything.
I would have offered to pay but he just did it. And we're still friends. He could have been a dick or dealt with it. Nothing I could do. He dealt with it.
Maybe ask the old man to go halfs on a fence.