Ok all kidding aside if you want to stop it, you have to make her know you mean business. Get some rubber gloves, and get some of that dog poop. Now you go to her house late one night and you put a little of that poop under her car door handle. Then you leave the picture with a little note on the back. Here are some of my choice notes:
1. "Seems like you left something at my house"
2. "And I thought stepping in it sucked"
3. "Do you smell something?"
4. "I don't fertalize your toilet so don't poop on my lawn!"
5. "Something funny about this picture, just can't put my finger on it"
any others that you can think of, would be great too. If this fails, well then next time you see the person walking the dog. Walk up behind the dog, an with all your might, kick him as hard as you can in the ding-dong. Things should get better then, your lawn will be greener then ever!!