wwyd man letting dog poop in yard.

So we have a couple pepole who walk their dogs in our neighborhood. One is a lady who always has doggie bags to clean up the mess. Well theres also this much older man that walks his dog without a leash and will let his dog poop in our yard. I caught him once as the dog was about to do his business and he called his dog off our lawn. We just got the grass growing again. Plus my dd walked in some last week. Its starting to get really annoying. I get dogs have to go but at least clean it up. So what would you do? Get a sign or ask him to keep his dog off our lawn? I just feel I shouldn't have to clean up his dogs poop or worry about my girls walking in it. I've never had this issue before. But im tired of picking up after someone elses dog.