185.15  Contributions; new employees.--Any person who enters the employment of any incorporated municipality of the state as a police officer after July 31, 1953, and who does not desire to accept the provisions of this chapter shall, within 12 months after employment, notify the officer or board paying the salary of such police officer, in writing, to that effect. Thereupon, it shall be the duty of the board of trustees to refund from the municipal police officers' retirement trust fund the full amount, without interest, withheld from such police officer's salary and deposited in such fund. Thenceforward no withholding shall be made from such salary and all police officers who have given such notice shall be barred from participating in the retirement system.