It is considered the polite thing to do, at the very least, to pick up dog droppings when you're in a public place or if out walking your and dog stops and leaves it in the street or a yard. I always have a couple of grocery (carrier) bags with me to pick it up and tie off the bag. If you think about it, it's a great weapon if you ever feel threatened when you're out walking (and having dogs with you isn't enough protection!) - swing or wave or throw the bag of dog waste. (It's easiest when our walks are on trash day to drop the bag in one of the bins as we walk past. Otherwise it goes in the trash at home. Everything out in the yard is picked up periodically and dropped into the compost.)