Or buy a massive dog and let it out whenever the others are on your property, all the dogs I've kept have always been cleaned up after, I can't believe people these days wouldn't look after them, slightly OT but the worst people are the ones who let the dogs off the lead in public places, where it either says dogs must be on a lead or there are small children around, it's alright them saying 'oh my dogs good with kids etc'butbtahts not the point, anyone who's met me will have seen the damage my own dog causes me,
A couple of years ago I had a really anti social dog who didn't like other dogs so the other owners only had themselves to blame when I'd have ago when it came sniffing