What locks do you use, chain or D.

it's as much about "how" you lock your bike, not what you lock it with anyway....

• if leaving bike more than 10 mins take front wheel off
  
• lock it somewehere visible...if possible where you can see it as well as passing public
  
• lock in an inaccessible place (up a lampost, high up a fence, wrong side of fence, in a tight gap)
  
• lock with your mates and use as many locks around as many bikes and and as many anchor points as you can.
  
  

never take it for granted that your bike is safe, no matter how expensive your lock....part of the reason my bikes have never been nicked is probably due to this attitude...buying an expensive lock might give you false confidence and at the end of the day a dtermined thief will still break a "top" lock.