How do I deal with someone who's been shitting in front of my house?

I’ve been seeing poop in a path which is connected to the gates of my house. This has happened 3 times now over 1 or 2 weeks. When I saw the poop first, I thought it must be a dog. But everytime it dries (every 3 or 4 days), a mysterious pile of new shit is dropped on the old shit. It’s (*very*) black, very smelly and in the EXACT same spot!! Right on top of the dried shit!! I’m convinced it’s a human being. I’ve decided I’m gonna hide in some bushes nearby and catch them doing the deed. But what do I do then? What if they don’t care and continue doing it? How do I make them regret it without getting into trouble? It’d be nice if they couldn’t tell it’s me.