At our house, we've been in the habit of calling out to people who leave dog shit in our yard, providing a bag when they claim they "just forgot" one, and generally giving the benefit of the doubt to horrible dog parents. The thing is, though, when we've forgotten bags on walks with OUR dogs, we've used anything we had on hand to clean up after ourselves- napkins, envelopes, leaves, whatever, in order to not be complete assholes. From here on out, no more leeway and no more warnings- if we catch you leaving feces in our yard, one of us will follow you home, take that crap you left plus any more we find in the yard, and smear it all over your front door. If that doesn't sound pleasant, then start cleaning up your fucking dog shit.