There is no any common law throughout the U.S. to enforce dog owner retrain their dogs with a leash, while owners walk their dog at any public places like park, neighborhood paths, streets, ...where usually have child or people playing or walk by.
We need a common law cover the whole nation with the purpose of protecting human not to be attached by dogs that caused by dog's owners carelessness and selfishness.
Whoever wants to own anything, they need to be responsible for it. Same as owning a cat. Owners can not allow their cats go to neighbor's backyard do their bowel movement everyday.
Cite to these pet owners will not just protect people, but also increase government income. Anyone can transmit photo images to the city they live with the registered dog's owners file for citation.