A mountable lock includes a lock body and a retaining member. The lock body is configured to be secured to an external structure by at least one fastening member. The lock body includes a lock interface movable from a locking condition to an unlocking condition in response to proper user manipulation of the lock interface. The retaining member includes a first end receivable in a first opening of the lock body and lockingly engageable with the lock body when the lock interface is in the locking condition, the first end being disengageable from the first opening when the lock interface is in the unlocking condition. The at least one fastening member is accessible through a passageway in the lock body that is blocked when the retaining member is in locking engagement with the lock body, thereby preventing disassembly of the lock body from the external structure.