Of course, you could ask the neighbor to keep their cat out of your yard, but unless they are going to keep it indoors only, that won't happen. In effect, you'd be asking them to keep their cat indoors, which might seem a large demand.
On the other hand, it's strange that someone should accept that the neighbor has a right to keep a pet that poops in your yard, and worse, in a place where your children play.
When I was growing up, we did have a sandbox, and neighborhood cats would poop in it. My father wasn't fond of cats, and he would put out a raccoon trap with tuna, catch the cat, and then drive it to the pound. I remember feeling conflicted about that as a kid.
We have a neighborhood cat that does poop in two places in our yard: behind our garage, and in one spot next to the house. I have no plans to catch this cat, or even to find and confront its owner. But I wonder if there are any deterrents we might try to change its mind about pooping in our yard. Like pepper powder or something.
Try it out. Report back.
Scarecrow Sprinkler! http://landscaping.about.com/od/helpforconsumers1/gr/scarecr...
Is there any equivalent for cats? What would scare the crap (pun intended) out of a cat? Are cat's too smart to fall for something like this? Maybe you need a real, live dog? You can have one of ours :-) Your choice.