A flexible insert or guard has an elongated plastic body having a length to cover an opening of an electrical box and having two prongs or posts extending outwardly from the body for insertion into spaced apart mounting holes of the electrical box. The elongated plastic body flares outwardly at its ends in a region of the prongs and narrows along a center section to provide a gap between the insert and side walls of said electrical box wide enough to allow the insert to be removed after drywall is installed.