Running your dog on school grounds, sports fields, playgrounds, and other fenced public areas that are intended for human recreation actually can pose a great public health risk. Even if pet owners pick up their dog's feces, the grass is left contaminated with fecal material (bacteria and parasites). Just a couple of dogs visiting the same field on a regular basis can contaminate an entire field in a short period of time. These fields are then being used by people who sit and play on the same contaminated grass, the most concerning of which are children with developing immune systems.