What I'd do. (Score 1)

What I would personally do is post someone at the entrance (if there are multiple entrances, have them covered as well) and make a log of everyone that comes in and what equipment they brought (and have a sharpie and possibly some stickers to put on equipment). I would also require them to sign a log book that states that "the signed below agree that any lost or stolen property is not the responsibility of the party holder." The list of equipment is to make sure that no one can say "that guy stole my thingy!".