If the crowd gets out of hand, they can fire on them with anti-aircraft guns.
ROFL ROFL You freepers are NUTS! ROFL ROFL
ROFLOL! Or have one of those shipping container cranes periodically swoop down and knock the pesky troublemakers into the water.
Loudspeaker: "Cleanup on Dock #4 needed."
I guess we could throw them some life jackets. I won't be too mean. ;-)