There is a reason that the National Park Service has a posted rule:
ALL PETS MUST BE KEPT ON A LEASH
No matter how precious, friendly, darling, and good-with-kids your man's-best-friend is, keep him on a freaking leash when you're in a public area. You have no idea how your dog will react in every situation, or how long your "friendly" puppy that you let run ahead out of sight is going to keep another family with kids at bay growling, snapping-teeth, and lunging, while you are lollygagging behind, chatting with your girlfriend (long enough for a family to corral both kids on top of the stroller and make several attempts to scream "GO AWAY" to the idiot-freak dog who wouldn't leave).
The proper response when said family informs you of NPS policy, not to mention Fairfax County Law, is not,
"I'll raise my dog, you raise your kids!" and
"Mind your own damned business!"
People like you, with complete disregard for others' safety, shouldn't be allowed to raise dogs. Besides this, you were in a WATERFOWL PRESERVE! WTF were you thinking? With an unleashed dog! What if your dog killed an endangered waterfowl species? Moron!
LEASH YOUR DOG ALREADY!!! bitch. I'm bringing my mace next time.