Why does everyone have to complicate this so much? In the area where I live, I just ask one question: "Would you care if I did a little metal detecting on your place?". Most folks around here, if they say yes, could care less to see your finds. They care more about whether you do a good job filling your holes. Often, they will volunteer information like, "There used to be an old house over there." or "There are rumors that the previous owner buried some money here somewhere.". If that's the case, I'll usually offer to show them if I find something that interesting.
Also, if the owner comes by and asks, "Find anything good?", I'll usually empty my pockets & show them. Otherwise, I don't go out of my way to show my finds unless they've asked me to beforehand.
I have one place where I've agreed to relinquish all of my finds (it's the property of the local historical society.) & I've been completely honest with them. Haven't really found anything valuable, but a few neat artifacts.
Just ask, be polite, and be thorough filling your holes. Easy as that. I wouldn't go shoving contracts in folks faces or start discussing sharing valuables, etc. It scares a lot of people off or makes them think you're in it for the money rather than the hobby.
Good luck!