Well, I see it this way. If you can't use your yard because of the cat feces, then I would call animal control. I love cats, but if I had one routinely using my garden as a litter box, it would make me mad. Their urine and feces have an overwhelming odor and can carry diseases such as toxoplasmosis.

I would not chase the cat, but I would photograph it pooping and hunting on your property, as many times as you can. Then you have a little ammo, and it isn't just your word versus the neighbors'.

If it's the wild cats, I would bait a "Have a heart" humane trap with some wet cat food, catch it, and take it to an animal shelter. (They don't normally adopt out feral cats, though, just so you know. They are ususally euthanized. So, maybe a no-kill shelter for the wild cats if that bothers you.)

Anyway, those are my suggestions.

Good luck!