Abstract: A device helps prevent contamination from reaching the inner workings of a computer trackball assembly, thereby prolonging intervals between maintenance. A circular ring attaches to the exposed surface of the panel through which the trackball protrudes for use, preferably to the retaining ring typically used to hold the ball in place. In cooperation with this ring, means are provided for preventing contamination from migrating below the panel surrounding the ball, thereby helping to keep clean the inner workings of the trackball assembly. In one embodiment, the means cooperating with the circular ring includes a second ring of material having an aperture with a diameter dimensionally configured to wipe against the outer surface of the trackball during use. In an alternative embodiment, the means cooperating with the circular ring includes a flexible dome of material entirely covering the externally exposed surface of the trackball.