Abstract: A device is provided for use in conjunction with a marine vessel having an engine, a transmission connected to the engine and having a portion extending exteriorly of the boat and an out drive which is connected to the exteriorly extending portion of the transmission by removable fasteners. The device of the present invention prevents the unauthorized removal of the out drive from the transmission. The instant device comprises a housing having a top wall, a back wall and opposing side walls which extend downwardly from the top wall and on opposite sides thereof. The top wall of the housing includes a slot through which the mooring eye on the out drive is positioned and, in doing so, the threaded fasteners which connect the out drive to the transmission are inaccessibly positioned between the housing side walls. The housing itself is removably secured to the out drive by a padlock having its bolt extending through the mooring eye in order to permit removal of the out drive only by authorized personnel.