If I put myself in that idiot's shoes, logically it would be best to confront the owner rather than the culprit itself. Luckily, here in Australia, pet owners possess a brain and common sense to do something about their own pet's mess. Therefore, taking the matter up to the owner would be effective to a certain level.
IF the culprit re-offends, I reserve the right to take the matter up to the Council and have them to deal with the owner, that would involve a certain degree of authority and they might have to pay a fine. Worst case senario would be revoking the owner's right to keep a pet if I take it up to the RSPCA.