I agree with those that said to come up with a deterrant. That cayenne pepper idea is marvelous. I had the same problem when i moved to my new house, simply "returning" the poop to the rightfull owners was enough to have the owners stop letting them shit on my lawn. I'm sure having the dog come home covered in it's own poop helped alot too ( I scooped some fresh stuff up in a shovel and threw it at the dog and sent him home covered in poop)
good luck :joint1: