I bought one of these mutha's:http://www.onguardlock.com/?page_id=329
It's 16mm thick and heavy, but is covered in rubber so it doesn't scratch stuff -ideal for lamping a would be bike thief across the head with
Used with a cable for the q/r bits; I have peace of mind that the average skuzzball will be deterred and move on.
£24 on Ebay
What I have noticed is the amount of dents on bike racks/railings - these, I'm sure, are caused by low lifes attempting to hold the lock firm & hammering/chiselling it 'til it gives way.. A fitting way to deal with their pinkies if you ask me.