A fence, wall or other structure at least 6 feet in height must completely enclose the swimming pool, spa, or hot tub, and must have horizontal supporting members located on the inside or pool side and be designed so as to not allow children to climb such fence, wall or structure. A fence, wall or structure enclosing a swimming pool, spa, or hot tub may not have any openings, other than doors or gates, larger than 4 square inches. Fences comprised primarily of vertical members (i.e. picket type or wrought iron) may not have openings between members, measured horizontally, greater than 4 inches.