I certainly wouldn't use any regular sort of lock, as I can break them open rather easily simply by spraying deodourant in them to freeze the lock and then I simply break it open. If anyone else is as smart as me then your bike is at risk! Personally I use a heavy duty chain which is extremely hard to break, even with a pair of bolt cutters. Also locks are good fun for locking people in their houses, I did this to somebody who lives near me the other week and they had to call the fire brigade to let them out
