I use a 1/8" leash to lock the seat, a pretty meaty cable to attach the frame and wheels to whatever I'm locking to, and a U lock to attach the frame. A pro thief could steal my bike in a couple of minutes, I imagine, or just steal the seat - but my bike looks pretty beat up, and my seat isn't high-end (although it's comfy) so nobody wants it anyway. I figure you want to put enough locks on to make it more inconvenient to steal than the nice bike next to it