When the city council has approved the final plat, the signatures of the mayor and city clerk shall be contingent upon the receipt by the city of a guarantee from the owner or subdivider to assure the satisfactory completion of all the necessary subdivision improvements. The form of guarantee shall be a certified check or cashier's check, letter of credit or surety bond, as directed by the city, payable to the city at one hundred percent (100%) of the cost of the necessary subdivision improvements as estimated by the owner and approved by the city engineer. If the owner posts a surety bond, it shall have good and sufficient surety therein and shall be approved by the city attorney. (1988 Code §9.115)