Wow, Velocivixen, glad you're okay, that would be scary.

My previous rack had the rails, flat section and the angled portion toward the front of the bike. Occassionally, I use to carry the lock flat on the rack and use those webbing cinch straps, I always felt a little more secure and the lock rattled around less.

Now, with the slimmer rack, and since I'm only doing commuting or errands, if I carry the lock, I'll put it in one of my Ortlieb bags, with the bag flattened out. On rarer occassions, I'll throw it in my messenger bag.

If you have extra money, I've seen a leather u-lock holster that straps to the side of the rear rack - of course, I'd be afraid someone would steal the holster.