Most locks that are designed to secure your bike in public are usually U-shaped and have funny-shaped keys, but if you feel that is not secure enough, try the Forever Lock. It has a great design for added security.
It hides the keyhole out of reach, so that it can’t be accessed with traditional lock picking tools. You have to insert the specially-designed key inside of the mechanism, through a combination of actions. It’s sort of like a puzzle game, but easier to solve. The video explains it better:
You can’t officially buy one in the U.S. market yet, but according to the guy in the video, he is selling them for $140 each if you contact him. Seem expensive? Sure, but if you’ve got an expensive bike, this is a super secure lock, and short of a thief using a blowtorch to cut it, it’s not getting opened by crooks.