My question involves real estate located in the State of: California

An older friend has 40 acres on top of a hill. He and I, along with some other friends have built and licensed a small radio station with tower and small building. He and I would like to somehow secure the future of this corner of his property for the long term, to pass to our friends, after we are both gone. What would be the mechanism/document(s) for doing this? I've heard of 99 year leases, easements, etc..... Something that would still be in place if the property changes hands, either through him having to sell it or his passing away. Something that would still be attached to the deed after we are both gone. Thanks!