National Parks & Corps of Engineers properties....
As far as NATIONAL PARKS are concern, it has always been against the policy of the National Parks to allow metal detecting and excavation within the Park's boundaries due to the nature of the Parks being established to preserve historical and archeological heritage in those sites that are deem "National Park Service" lands. Since 1999 there was a new ruling by the National Park Service that was started after the Shiloh incident whereby they now can arrest you for "Suspicion Of". Thus opening the door to many interruptions as to if your intent was to steal artifacts or not, even with your detector locked in the trunk of your car. Several have already fallen to this new ruling. Best to keep your detector out of site and broken down if it happens to be with you on a trip to a National Park somewhere. These rules are in most of the National Parks hand-outs to be read by all. I doubt a letter of permission will go very far when they give public notice in their literature.
Now for the ARMY CORPS OF ENGINEERS properties, I have been in on since the very first of the making of a nationwide policy in March of 1989. On my website I have the original policy memorandum sent by the Corps in Washington DC to all Corps district offices on that date. In short, the memorandum requires all Corps district managers to designate open areas in their regions for metal detecting, but subject to the Corps Project Engineers. Most are allowing beaches, swimming areas, volley ball courts, camp grounds and etc....."Public Use Areas". If at anytime someone has a problem with any Corps ranger, do not argue with them, contact me! I have been reporting to the Corps office in Washington DC since the national policy began, acting as a go-between as you will. Between myself and Cheif Darrell Lewis of the Corps, we have been very successful in solving all problems to this date. I assure you the Corps loves us, for we clean their park areas better than their own employee's as so stated by the Chief. Since 1989 national policy was created, I have offered to all, free copies and I will pay the postage of the paperwork and permission of this policy. If any of you wish a copy, please just email me your address and I'll get it right out to you. We are updating my website to show better copies of the same and it should be finished soon. Please feel free to contact me at anytime about any problem or information you need about the Corps properties.Thanks you, Keith R. Wills