Outside of the Great Smoky Mountain National Park properties which you cannot metal detect in or take anything out of, getting permission to hunt private land is somewhat hard to do. This is mainly due to non-locals coming in and buying up and posting the land and also because many locals are distrustful of outsiders! I have mentioned this before but don't know if anyone took my advice. All rivers and streams outside of the National Park and National Forests in they are natural and have native fish and other aquatic life in them, belong to the State of Tennessee. Therefore, you can enter any river or stream from public access or land and walk the entire length of the river or stream as long as it does not enter and flow through any part of the National Park or National Forests and as long as you do not get out of the water or their' normal banks. Therefore, I believe that you can metal detect any and all sand and/or rock bars within a river or stream as long as you abide by the above stated conditions! There were many, many flash floods and floods in the 1800's and 1900's up until probably the 1960's, especially up until the 1950's, that washed a many a home, church, business and other outbuildings away from Gatinburg to Sevierville. Some folks lost everything including coins, precious items as well as necessities of life and these went down the rivers and some larger streams. Therefore, it is quite possible that someone might metal detect and find some of these valuables and non-valuables stuck in the many sand and/or rock bars that can be found along some of these rivers and streams. If I was looking for some better places to look in a river or stream, I would start trying to find sand and/or rock bars in the Pigeon river from below the National Park boundaries upstream from Pigeon Forge all the way downstream to near Sevierville. However, I will give you a few words of caution! First, the river has many deep holes and possibly sink holes, so if trying to metal detect a portion of a sand and/or rock bar that is in the water, don't venture too far out as you could easily slip into or be pulled into a very deep pool of water. Also, if you are angrily confronted by a property or business owner, just walk away but if in doing so, the property or business owner escalates the confrontation, then call 911 to have Law Enforcement come out to de-escalate the confrontation, access the situation and advise you on whether or not you can or cannot continue your' quest.
Also, keep in mind that many Native American Indians lived along the stretch of this same river from the upper end of Pigeon Forge to Sevierville and beyond. Therefore, it is quite possible to find arrowheads, spear points as well as many other items such as tools used by these early Americans!
Good luck and as always, be safe!
Frank