If possible, you folks should considering doing what the SCCA does, they offer "day memberships". With that, you still keep your insurance regulations and you will not destroy your walk-ups. Right now, I can almost promise that 99% of your walk-ups will disappear and any of the folks that do it casually will probably disappear also if they have to get a full membership. With a day membership, you charge a little extra, have the folks sign some documentation and everyone is happy.