It's simple really. Just file a UMA policy with the land owner.
That's what happened when an AMA club didn't like the idea of an SFA club using a county owned field. We went to the county comissioner and filed a SFA policy along with the AMA one.

For some reason, the AMA club still didn't like it, but couldn't do anything about it. For what it's worth, the county officials stated that no extra policy was required, not AMA nor SFA, as the county had their own policy, but if they club wanted to file, that was fine with him. He said that it was a public park and anyone could use it as they wished, within reason of course. As far as law suits, he said they had many from ball players, spectators, and people tripping over painted lines in the grass. One kid was even several injured playing littleleague baseball.

Take care,
CCR
http://www.kites.org/rc_instructors