Have you thought about ring locks? I'm about to try one on the bike I'm building up to replace my current commuter. It's not a total solution, but I think it makes sense as both part of a layered defense and as a quick and easy lock that is always on the bike, and doesn't have to be carried on your person. Combined with a chain or a u-lock (that you might leave at a usual lock up location much of the time) it makes your bike a tougher target than most neighboring bikes and since it takes care of the rear wheel, you might be able to get away with a lighter lock that you use to secure the bike to something and maybe the front wheel.


This is the Axa Defender, you can get an accessory chain that plugs into it, and Abus makes a very similar ring lock, although not a chain AKAIK.