Invest at least 10% of your bicycle's value in a high quality lock.
Here at Electric Spokes, all of us have at some point in lifetimes, have had the awful feeling of being robbed. Nothing hurts more than seeing the empty space where you last parked your bike. You hope that you were mistaken - that you didn't park it there, and that maybe it isn't stolen. Of course, you eventually come around to the realization that you've been robbed.
It's an awful feeling. What might surprise you is that any reasonably competant thief can break or bust through any lock. It's a matter of tools and time. Today's thieves can cut through any type of metal using a portable electric cut-off saw, cro-bars, cable-cutters, or even a little pocket dremel tool. It doesn't matter the strength of the lock - given enough time, any competant theif can and will break it.
But you definitely have some . See this video below to watch it in action.