bridging plate 70 is then inserted over the lower stretcher plates 66 the spring means 42 is coupled to eye 44 of the anchor upper end 30 and to the adjustable eye bolt 46 the upper end of the eye bolt 46 is passed through the central round opening 74 of the bridging plate 70 a distance sufficient to permit wing nut 48 to engage the threads of bolt 46 the wing nut 46 is then tightened so as to apply the desired pressure to the post 10 another bridging plate 70 including the bolts 52 and retainers 82 is clipped to the upper stretcher plates so that the upper ends 84 of bolt 52 project beyond the upper end 14 of the side assemblies 54 a pair of side panels 86 are then slidably received downward from the top 14 in confronting slots 56 of the two adjacent side assemblies to complete the enclosure 12 except for an upward facing opening the mounting board 50 is then positioned on the top 14 of the post so as to receive the upper ends 84 of bolts 52 which together with fasteners such as nuts 88 act to secure the mounting board 50 once.