They sell this stuff you can spray on your grass that deters animals. It doesn't hurt them or anything. It's by the mouse traps and insect killer at lowes near me lol. As a pet owner, I would be completely fine with my neighbors using this. Then again, I have enough respect to pick up dog turds.

call the cops

Buy a toy poodle, and every night, go over and shit on his porch. When he confronts you, say "twinkles has the biggest poops" an then get your friends to poop on his porch too. He'll be too confused to retaliate

taze the damn guy!

Get a shovel and fling it all back over the fence

It's actually illegal in most states to not pick up after your dog. Call the cops for "suspicious" behavior and tell em some creep comes by every day.

Don't know what to do? How about "The next one of your dogs to be led into my yard is gonna get a screwdriver through it."

You deserve it for calling them piss-pipes and poop-chutes. I'm sorry, but there are much more accurate terms for these.

pellet gun

Haha go buy a dog and let him relieve himself in your neighbor's yard :)