Contractors licensed hereunder shall maintain their equipment and work areas in a safe condition.  All debris shall be contained on the site and disposed of routinely.  All openings and excavations shall be well marked or covered.  Curbs and sidewalks shall be planked sufficiently to prevent damage before any heavy equipment is moved across them.  Dirt or mud that is dragged into public streets must be cleaned daily.  All contractors licensed hereunder must show proof of license before a building permit is issued.