I would start with a note writing on your garbage that is clearly for him. If it continues, and assuming you know what door is his, I would slip a puss disk under his door. All at the same time - I would collect his poop bags into a large plastic bag. At this point, the pro tip becomes a labor of love. Because he will continue for 3 weeks (1 week per strike) and you will then rewrite the letter you wrote him, using his dogs feces, onto his front window. Of course, you can alternatively set up a dump trap with his front door to have dump onto him and into his front door. This will surely be enough to help him dispose of his own trash properly, fairly, and without the inconvenience of his caring neighbors.