There shall be constructed on or near the property line, or next to the developed commercial parcel, opaque ornamental fencing or evergreen planting, which will meet with the reasonable approval of the adjacent residential property owner so that such material or commercial use cannot be seen by a person standing on ground level in a residential district when located to the side or rear of the lot on which said open storage or display or use occurs, provided however, that screening shall not be required in excess of eight (8) feet in height. Notwithstanding any requirement contained herein, the abutting property owners may agree to modify or waive the screening requirement, such writing to be filed with the City Clerk. Unless special permission is granted by the Board of Adjustment, such fencing or ornamental screening shall be in place prior to the commencement of construction activities upon the commercial lot. All planting shall be kept neatly trimmed and fencing shall be maintained in good condition at all times and must act as a sight barrier for the benefit of the residential district. Merchandise and materials which are not completely assembled, or which are not immediately and actively being offered for sale, shall, in addition to complying with the above screening requirements, be so screened by ornamental fencing, evergreen planting or permanent buildings so that such material cannot be seen from a public street. The provisions of this Section may be modified or amended by the Board of Adjustment, whose determination shall be final.