“edge of the grass” sounds like “edge of the road” to me. Where else does grass have an edge that horses riding down the road can poop on?
OP, I encourage you to take a step back. A righteous war in your mind may ostracize you from every neighbor around, who apparently don’t have the same issues as you do. You may need their help some day. Stop worrying about the horse poop, focus on fixing this place up and go back to suburbia, perhaps. ETA: It’s probably too late for the ostracizing though honestly, as I’m sure everyone talks and you’re known as a city slicker whiner already.
This is why I said from the start that this is not the hill I’d pick to die on here.
Analogy: I don’t have to hit my brakes to avoid being side swiped by someone who didn’t check their blind spot, but I do because it’s easier than dealing with the alternative. I was in the right, but it doesn’t matter. Path of least resistance.