Abstract: Trailer theft is a widespread problem, and existing locks have failed to solve the problem for a number of reasons. Some locks require permanent modification of a trailer jack, while others are easy to break into. The present invention provides a detachable trailer jack locking assembly including a retention shell couplable to a trailer jack body. The retention shell is sized and shaped to surmount an upper end of an outer tube of the trailer jack. The retention shell also includes a slot configured to accept a handle of a lifting assembly on the trailer jack. The assembly includes an attachment point disposed on the outer tube of the trailer jack. A lock is adapted to secure the retention shell against the outer tube by coupling with the attachment point. When engaged, the handle is immobilized within the slot, thereby rendering the lifting mechanism of the trailer jack inoperable.