Back in my college dorm days, we had a large 8' high metal gate that provided an opening between 12' block walls that secured the dorm area. The gate was right outside our dorm suite, and it was locked promptly at 10pm daily. This required any visitors to detour to the main secured entrance several hundred yards away.
Well the local pizza delivery guys decided that late night pizza orders were easier to deliver by hopping over the lock gate. This resulted in lots of late night clanging noise as they scaled the high gate. After being woken up one too many times, a liberal application of never seize, axle grease, and powdered graphite to the top rail of the gate solved the issue! We had a good time watching the first few idiots jump up to scale the gate and stomp away in frustration looking like a tin man!