There shall be erected and maintained a good quality split, sapling, stockade or PVC picket fence, five feet in height above average grade, enclosing entirely the area occupied by such pool, except that no fence need be erected along any boundary of the pool area abutting on any wall or walls of the main building on the premises, provided such fence and wall or walls completely enclose the pool area. The pickets shall be erected vertically and shall be butted against each other. The distance between such fence and the nearest street line bounding the premises shall at no point on such fence be less than the distance between such street line and that point on the main building on said premises nearest such street line.