Buying land from aging parents

[Athens Matt]

Hello all!

Not sure the right place to post this, my apologies if this is the wrong place. 

My father in law and I worked out a deal between us to allow me to buy a piece of land from him. Basically I do the labor and up keep, help him with cutting and splitting firewood from the land, and cleaning years of trash dumping on it by him; in exchange for ownership of the land in 10 years. About 4 or 5 years ago he had a health scare and once through it we decided to write our agreement and each sign it. He was scared if he had died or gone on medicaid assisted living my family would have lost the land. Thankfully nothing happened to him, forget the land, I love the guy!

Okay so now he's having some trouble again and wanting to come over and discuss how to ensure my wife and I retain the land, we don't have enough money to buy it for cash, or loan, for market value nor a reduced cost for work done already. He's very concerned the state could take it away and because this land was his parent's land, now his, and he wants it to become ours and later our son's, he's very concerned modern laws will stop this. 

What is your advice to help us ensure this land stays in the family like he wants? My credit and my wife's credit is good but there is no way we can afford monthly payments on this land. We can find a way to pay for the taxes annually on it but really that's about all. Does his and my agreement stand for anything with the courts? 

Thanks!