I learned something important from a subway construction crew tonight. The upside down Us that we all lock to on the street are very very insecure. All it takes is a ratchet to take them off of the ground, rendering our fancy ulocks and chains pointless. But there is hope. If you lock to the same U regularly, bring a tack hammer next time you lock up. Enough of the bolt protrudes beyond the nut that you can bash it down and prevent the nut from being removed. If you have no hammer handy, eschew these seeming oases of security and lock to the nearest secure pole.