This will keep that dog out!

There's Far Side Cartoon in which a guy is standing on the great wall of China. The caption reads something like, "This will keep that dog out!" I've thought about that lately as I have been finding, shall I say, evidence of dog presence in my yard. I have a small yard, so if there's something disgusting to be stepped in, there's a pretty good chance somebody is going to do it.

I've been casing the neighborhood, and I have a suspect. His name is Toto, and he's what you'd expect. Small. Annoying. Able to bite the hands or ankles of witches and hapless neighbors. In the most diplomatic way possible, I have approached Toto's owner and explained to her the problem. I even showed her the convenient location I keep the scooper contraption. Does Toto continue to use my yard as his potty? Yes. Does Dorothy (not her real name) clean up after her beloved pet? Of course not. One begins to sympathize with Mrs. Gulch, that misunderstood villain who's just trying to protect her precious cat.
Other than erecting a smaller version of the China wall, I'm at a loss as to what to do. The sneaky critter seems to know when I go to work and waits until then to leave his deposit, though there have been a few times on the weekend I've caught him with his beady eyes on my side of the street looking all smug, sniffing around trying to find just the right spot in which the unsuspecting mail man will cut through the grass, put my mail in the box on the front porch, and leave smelly footprints on my outdoor carpet. Or worse, my son's poop magnet shoes will continue to work their magic, and I have to clean up Toto's infraction from the tiny ridges of size 13 kid soles.
I like my neighbor. She's a decent person. I don't want to create neighborhood strife by "accidentally" running over any small dogs on their way across the street to poo in my yard. I don't want to lose the neighborly contentment we share by calling the police on her pooch. And, honestly, don't they have better things to do anyway?
The best I can hope for is a well timed twister which will carry Toto's furry tail somewhere over the rainbow.