Wish I could have read the whole thread, but I have other volumes to read. I read the first several and the last several pages.
It seems these are the facts:
Frankn has info on a cache.
Frankn will take >33.3% or nothing at all.
Frankn believes that if he gets nothing, neither with the landowner.
Frankn has other, bigger leads to occupy his time.
Frankn has time on his side.
Landowner knows Frankn is interested enough to spend months researching this cache.
In my estimation, Frankn, you need to create the following three conditions in order gain your permission to hunt:
First, you need to get the landowner to relate to you. Fact: doctors with great bedside manners get sued FAR less than doctors with poor bedside manners, despite quality of care. What's this have to do with negotiating? Being personable, or at least appearing so, is everything in negotiations. If there's hostility, you've already lost.
Take the man out to dinner. Meet the wife. Share some crazy stories about family/friends, but also about sweet caches and long, long hours researching in dusty library books. Appeal to his emotional, imaginative side. Be sure to ask about his life. Show him you are a professional, but also a personable fellow. This first point alone could seal your deal.
Second, you need to limit the owner's ulterior solutions. Help him understand that he can't find it without you. You have all the information on how to do that, but make it clear to the landowner. Or help him understand that his ulterior solutions aren't as cost-effective as yours. He is an investor, after all. Assume he's a shrewd man. Convince him that you are his best investment.
Third, you need to create some sense of urgency for the landowner. He doesn't want to keep his 9.5 acre investment property forever, he wants ROI. Figure out when he's going to flip it, develop it, etc. That's important leveraging information, and gives you a timeline. He may also need some kind of expiry date for your offer. Speak his language: let him know this is an investment for you, too, but that you're not hung up on it (read: He can't wait you out because of your sunk cost). Depending on your read, you might also indicate that your offer will depreciate by 3% when you contact him in a year, and that after 11 years the offer will expire. When faced with the long view, people often become more myopic. Hey, you can hope, at least.
If you can do those three things, you'll get the deal you want. If you take my advice, and succeed, then donte 1% to a charity in my name, would you? ;-)
Best of luck, Frankn!
-Ammo