I second the anchor bolts. You can choose one of a number of types, including those that can be bolted or screwed into wood, concrete brick, etc. There are a number of ways to make the screws or bolts resistant to removal. In my garage I screwed a large eye-bolt deep into a wall stud so I can cable-lock my bikes as a deterrent to would-be teenage thieves. Removing it with the bike attached would be difficult. Two eye screws attached to the same cable lock or U-lock would be impossible to unscrew since each would prevent the other from rotating.