Get permission. Some graveyards and cemeteries are privately owned and not open to the public. Check with local officials to make sure it's all right to go in the cemetery. Also check if headstone rubbings are allowed. Some states have banned this practice because of damage that can occur to the tombstones. Damage occurs when a brush is used to try to clean the lettering and wears away the writing. I realize cleaning to make clearer pictures is an act of kindness but makes for some unhappy folks.