The board of any park district may employ engineers, attorneys, clerks and other employees, including a police force, as may be required, and may define and prescribe their respective duties and compensation. After receiving a certificate attesting to the successful completion of a training course administered by the Illinois Law Enforcement Training Standards Board, the members of the board and all police officers appointed by the board shall be conservators of the peace within and upon the parks, boulevards, driveways, and property controlled by that park district, and shall have power to make arrests subject to the provisions of the Park District Police Act. The exercise of such authority shall not permit the possession or use of firearms by members of the board.