Locks that work

singspeed I think in London at least, professional thieves DO carry the extra long boltcutters, and some have angle grinders. There's a photo somewhere on this forum, maybe even this thread, of some middle-aged guy with boltcutters in hand, and pilfered bike in the other. 10mm chains are not up to the job, unless the owner has huge luck, like you do.

Well, my reasoning is that even the strongest lock in the world will be broken by a determined enough thief. Half the good luck is created by judging where to lock your bike.
-I take mine indoors and onto the grounds of wherever I'm visiting as much as possible
-Avoid ever locking in the street except to pop into the shops for 5 mins.
-Uglify my bike with a horrid top tube protector.
-Park it out of view (e.g. if there is a bike rack, I will look for the rack with the sexiest looking bikes and park it among them where it is not immediately noticed. That way, a thief won't go for mine first!
-Take it inside if I'm visiting a friend.
-Take it and park it inside a friend's house if I know anyone who lives near where I'm visiting, and walk the 10/15 mins to wherever I'm going.
-Physically walk my bike around with me if I'm in a dodgy area.