In this litigious world we find ourselves living, I've found that giving someone Something with all that legalese on it, just puts them off.
A simple, written, signed letter stating that you assume all responsibility for anything that happens to you and that you will hold the owner completely blameless. Just has a better chance of working.
This farmer is a lost cause and I'd push no more. But do attempt to keep as a friend, with no hooks!
Maybe make him a nice display box of interesting things you found on his property. Give it to him as a Christmas gift. Then, let the chips fall where they may. You might even get invited back sometime.
Oh! And also? This farmer got talked into his action by a neighbor or something? Tell him, "Oh! By the way? I saw your neighbor on your property when I was passing by late one night. He was digging massive holes!"