I am now looking for an answer for my cat's neigbour pee and poop. I have seen the cats peeing and pooping in my backyard. They don't dig their poop.
The neighbors association from my neighborhood has a webpage were several neighbors have complained about the cat's problem.
They leave a very unpleasant smell all around any person's house. I have a dog. I've been having very bad odors before having a dog (don't try to blame my dog). I don't take my dog to walk and poop in neighbors gardens or front yards. That's being very unconsiderate as a neighbor. If I were your neighbor, would you like me to take my dog and let her poop in your garden or yard? And leave the poop?? I don't think you'll like it.
I don't have any problem with any neighbor if the dog or cat pops and they pick the mess. The problem they don't pick the mess. They are animals, I recognize that but they have an owner.
If I were you, I would take responsabilities over my cat. People who don't have animals don't have the responsabilities of picking and cleaning someone else poops from their backyards. You have your rights over your property and him have his. I think he's letting you know about the problem in a wrong way. But still, you are the problem, not him.