There is no lock or locking device that is safe from criminals. Nearly every facility I have worked in the last ten years use "security hasps." They come in about ten different colors and have been used by the FBI for trucking companies as trailer seals. Most management companies use them along with auction locks. I give them to tenants that might not be coming back to their unit for some time. I make it a priority to check the hasps every time I do a "lock check." Every manager should be doing a walk-through of their facility at least twice a day. When you print out your walk through list simply highlight the units that should have a security hasp. I started this for military people that were worried about their belongings being stored for a long time.