Sadly, I'm afraid there is no answer.
There are all sorts of claimed remedies from special plants to Lion Poo and fancy chemicals.
We have the same problem and have yet to find a solution.
The thing is they come at night when you can't see them.
Apart from getting a dog or security guard there is no real cure.
Sorry......................
next time you see them (pooing or not) turn the hose on them. It won't hurt them, but cats hate water. Chances are you won't see them again. But if any do show up, just hit them with the spary them again.
buy a rat trap and trap that cat...good luck..of course, get something in that trap like cat nip or something cats may like..then drop that cat off about 60 miles away...