When I was a kid, there was a house across the street that whenever the grandmother would watch the kid, she would let the dog out loose and it would shit on everyone's yard. They asked her to keep better track, she didn't.
So my dad bagged the shit up one day and brought it over to her to take care of it, and then my neighbor also came home at that time and was super embarrassed about it. Dog stopped shitting in other's yards, and the grandma kept track of it from that point forward.
Morale of the story, you have every right to take THEIR dog's shit, and put it on THEIR front porch, or THEIR yard, or wherever. And kindly let them know you don't appreciate it, and you will not clean up the messes of other adults.
@FlyingLow do you want it to be terrified of you? Just next time it comes up, be loud and abrasive and chase it away, make it know that this is YOUR turf.
Edit: Should clarify. I don't mean smear shit all over their house, I mean bag it up and put it on their front porch or door handle with a note, or knock and hand it to them. If you don't want to bag it, shovel it across the street onto their property.