A lawyer giving something away for free? That’s right.
Attorney Bert Krages has a free downloadable guide explaining your rights when you are stopped or confronted for photography. You can also get a legal handbook for Photographers and information about photographer’s rights in the UK and Australia on his site. (Bert Krages Photographer’s Rights Page)
There is also a lot of confusion about tripod and flash rules in national parks (sometimes even the park service employees don’t know the rules) Print out this information and keep it in your kit for your next trip. Side note: most of the monuments in Washington DC are under the control of the National Park Service, but a different set of rules applies to the White House- so check before you go.