When required by the Commission, a cash bond or other financial guarantee acceptable to the Law Director shall be placed on deposit with the Finance Director of the City, prior to the Building Commissioner issuing a zoning permit in accordance with the approved site plan, to insure the improvements, such as landscaping, parking and sidewalks are installed in conformance with the approved site plan. The bond or guarantee shall equal the construction cost estimate of the improvements based on an estimate approved by the City Engineer, plus twenty percent (20%) of the estimate in lieu of increased costs, and shall be for a period not to exceed two (2) years and provide for the complete construction of the improvements within that period. Such performance bond or other financial guarantees shall be returned to the applicant only if and after the certificate of occupancy is issued to the applicant.