Abstract: The present invention is generally an anti-theft device, or locking mechanism suitable for anchoring a paddleboard to a fixed object. The locking mechanism may include a support body configured to engage with a fin box of a board such as a paddleboard or surfboard. In exemplary embodiments, the support body includes a cubical frame with one or more openings—for example, an opening on each face of the cubical frame—that enables a locking means, such as a lock or lockable cable to engage with the support body. Because the support body can be securely attached to the fin box of a board, when the locking means is engaged to the support body, the board will be secured to a fixed object, and unauthorized removal of the board is prevented.