Back up north, we had a municipal pool, and big changing rooms with benches. Upon entering, we were given a numbered, metal basket to place our clothes in. We were given a corresponding numbered tag-on-an-elastic-band. When we left the pool, we presented the tag, and were given our stuff. Would it be so difficult to set up a system to check back-packs? Make it private from the back of a truck...pay a dollar. Make it public, complete with cop, and bomb-sniffing dog. The trick, folks, is to ride the problem, not fight with it.