I feel for you. My neighbor did the same thing. He is always....out with the dog, an Irish Stetter, when he goes. So he had to be watching when his dog pooped in our yard.
For months this went on and finally my husband started throwing it back into his yard. Are two dogs are small and we have a fenced in area that their never out of, so we know it's his dog's poop. Finally he got the message. Believe it or not this man is a policemen.