Shitsenders.com for like $20 they will send a gallon bag of gorilla shit to their house. There will be a card hurried in it that they can see, but will have to get their hands dirty to retrieve. One side says "wanna know who shit on you?" This side they'll be able to read. The other side says "we will never tell" or something like that. Or scoop the poop, put in a bag, walk over to his house and hand it to him. Let him know that next time his dog drops a deuce in your yard you will be getting animal control and the police involved. If that doesn't work, follow up on your promise. Get video of his dog shorting in your yard and generally roaming the neighborhood. If its nice, remove its collar and have the dog catcher come get it. Put the collar on the guys front porch and take a shit on it. He will get the message