Speaking of Brooks B67/66, Champion and other sprung saddles, just realised that there might be room to slip the D/U Lock though the rails right like in that pic above? So this means one of the following is possible:

1) If it's like the one in Happy Pill's Post, you could slip a light weight chain (4-6mm links) through it and padlock the D Lock to the bike (and perhaps even round a pole supplying a further deterrent/obstacle for bike theft). Going with relatively light chain since I'm assuming it's on top of other setups I see which involves carrying a D lock to secure the real wheel and frame to the bike rack and the chain (say one with 11mm links) and padlock used to secure the frame and front wheel to the rack.

2) If the D lock is slim enough or there is enough clearence, and depending on the geometry (and seat height), you can attach the D Lock to the top tube of the frame? Even if it's a slim one, it's got to be better than using a cable since it can't be locked by simple croppers but would require something more heavy duty.

I wonder though, what is safer? A Slim D lock (say 12mm shackle) or a Slim chain and padlock (say with 4-6mm links). Can bolt croppers be used on a d lock with a 12mm shackle, or would it require an axle grinder/saw which is unlikely just for a saddle.

Oh, here's the post which got me thinking:
http://www.bikeforums.net/showthread...1#post12275129