Shooting on public property is a right guaranteed under the constitution. Have a copy of the constitution handy and offer it to them to read. Then have them cite the statute which prohibits you from taking the picture on public property, of public property. They can't do it. It just boils down to who has bigger balls. To add spice to the occasion, take their picture with a digital camera and tell them you are going to see your uncle the ACLU lawyer, and that your friend is running the video camera while you wear a wire for the FBI sting about civil rights violations in the park. Loads of fun. tim
P.S. On Memorial Day organize a shoot with as many photographers with tripods and cameras as you can find. Call a local news station to get it on film. Don't get mad, get even.