The guard is formed of moldable, flexible material and has a number of wheel-receiving wells formed in an in-line configuration in its upper wall. The forward and rear edges of each well are located high enough to prevent a wheel from rolling forward or rearward within the well. Laterally extending grooves are formed in the wells to minimize forward and backward movement of the wheels within the wells while the side walls of the wells contact the side walls of the wheels in order to minimize lateral movement.