Some people use two different type of locks that would take two different tools to defeat. I did find a lock that is a new design and it was given a gold rating which is the highest rating given to a lock, see: LITELOKŪ | Lightweight Bike Lock | Light Bike Lock | LiteLok It's a lot lighter than a U lock and seemingly a lot stronger having beat off an angle grinder whereas the best U lock took 70 seconds for the angle grinder to eat it.