Hmmm . . .
Everyone has their own and different views on this but here are a few of my ideas and comments on this subject.
1) Never start off by saying "I want to Treasure hunt or look for buried treasure" . . . to me that automatically attaches a higher than normal value to what you are looking for. I use the terms "metal detect" or say 'I want to look for relics possibly from the 1800's or early 1900's, anyhing to do with history." That way the property owner has to attach his value to what you are looking for.
2) The split . . . . a real tough one. Sometimes you may . . . . more often I pass on the property. However, I always tell them that if I find something of their personal or family property I would return it to them.
3) You can usually find the owner of property, even large property, at the local courthouse but it takes some time and effort. You might try the neighbor to the property and maybe get a name or contact for the property you are interested in. Permission for MDing on private property has always been a tough area. At least when you find the owner try to look sharp, be friendly, explain how you will work on their property, maybe give a small demo and then except their decision with a smile and a thank you. If you do these things and their answer is no at least you have a chance for a second chance at a later date. Maybe they'll decide differently later.
Those are just my ideas on it.
Hobo