Chicago has professional bike thieves. Take the bike inside.

That being said, we put two kids through college and grad school with bikes on urban college campuses that were rife with thievery. In about 12 student-years of parking bikes, none have ever been stolen. And that's leaving bikes outside 24/7. The bikes where nice, quality, but old race bikes. Custom built wheels, classy frames etc... but old. They were not walmart bikes.

Here's how we did it:

1. Set up bikes with pitlocks on wheel skewers and seat.
2. Krytponite U-locks (orange ones) that go through the frame and rear wheel. When bike was locked overnight, second U-lock through front wheel to frame.
3. When out and about, U-lock and a cable lock (or now Ottolock) through front wheel also to rack. This now requires the thief to have two different sets of tools to steel this. The tools for defeating a U-lock requires a grinder. The tools for defeating the cable requires a bolt cutter. Carrying both is a giant PITA for a thief.
4. Park the bike next to a bike that is poorly locked and preferably better than yours hence, a more attractive bike to steal.

We've given thought to adding one of the small cable locks that are also an alarm. That just adds to the PITA for the thief at low overhead in locking/unlocking.

The locking strategy is as important as the lock. Maybe more so.

That just makes our bikes more securely locked and much more complicated to steal and/or to take parts off for resale. Been successful so far. Last kid finishes his PhD this summer and then we're done!

J.