We had this happening on our road a while back, we thought we knew who the guy was, a neighbour (not one I know) followed him home to the next road to see where he lived, not sure what happened after that, but it seems to have stopped. As I have dogs, I was going out and picking up all this poo, sometimes about 10 piles of it in a long line, weren't my dogs, but couldn't leave it there, good luck, its horrid when these lazy gits don't pick up, gives all the good dog owners a bad name:'(