Compensating land owners

I am getting ready to have a discussion with a farm family who is considering working with me to develop a farm ed program on their property. My hope is to create a non-profit at their site, and have them be somewhat involved (as involved as they want to be). I have no idea how to approach the compensation piece with them. I was looking for ideas on what others have done in similar situations. They have a working farm but run no year round programs, although they are open to the public for various things. Do I offer a percentage of what I bring in, or a monthly "lease" payment? 

Thanks for your thoughts!

Pilar