Since we're discussing locking strategies --
If I'm using two locks, it's usually a U-lock and a chain. One locks the bike to a rack/lamppost/fence/tree, the other locks the unsecured wheel to the bike. Sometimes I use two U-locks since either lock is lighter than my chain; sometimes I just use the chain. I ultimately prefer the chain since I can lock up to just about anything. That way, I'm not SOL if all the bike racks are full.