Set the sprinklers to go off in the morning. Most dogs hate to get wet.
Put a few poison ivy/oak trees where the dog likes to poop. Hope he learns his lesson.
Make signs with giant pictures of ferocious looking dogs and put it in your front yard. Get some blow up dinosaurs and put several of those in your front yard as well. That might scare the dog.
Get a gnome and put a motion sensor in it. Put the gnome where the dog likes to poop. Program the gnome to say "NO! BAD DOG!" everytime it senses something. The gnome would preferrably wail its arms wildly as well.
Erect a maze on your front lawn. Hope the dog and owner get lost inside.
Build a catapult with a delayed weight sensor and modify the the end of the arm to be a flat 3x3 area board. Place this catapult where the dog likes to poop. Once the dog has finished pooping, have the device wait for 20 seconds, then fling that crap into the middle of the street. Hopefully it will hit the dog.
Build a pressure sensitive platform where the dog likes to poop. When the dog stands there, have a cage come down and imprison the dog. You'll be sure to find out who the owner is.
Learn to speak dog. Have a logic discussion with the dog about him pooping on your lawn.
Spend years learning the black arts. Summon mighty earth golems of great power to protect your lawn.
Lay down concrete.
dfi