What is the best natural repellent for keeping mutts from crapping around your shrubs and pathways short of a pellet to the butt?

If you can’t guess, there are lax owners who do not care where their mutts go when nature calls. Worse yet, there are too many of them to point a finger at. And if one did, their owners would swear up and down it was not their “precious pooch.” It had to be one of the other dogs. I figure I could invest the time and wait until I see one of the furry interlopers take a squat and ping them with a well-placed pellet, but my friends say that would be cruel. Who has a natural and effective method to keep these mutts away, hopefully around their owner’s shrubs and walkways?