Seeker, winter is the time of year I do my permissions. I have put together a binder with photos of finds, copies of written permissions with the personal information blacked out and blank permission slips. I only hunt historical locations now, but the binder shows a commitment to integrity it also shows that I document "all" my contact information. (This helps if they ever come back on you later)
I have a copy of the Morman gold coin auction story where a well documented (historical location found) $10 dollar gold coin went for hundreds of thousands of dollars and a less documented $5 gold coin at the same auction did not. I then explain the need for their end on any extreme find to help validate more value on the historical artifact.
I would add, "Never only get verbal permission" Always get written permission.
Bonus reminder, Any City Mayor can give you written permission for City Property as long as no City Ordinance prohibits it, at which case you get with the City Counsel.
"Yes" I've done this before...lol
Good Luck!
Stay Gold!
Opie