It shall be the duty of the police commissioners to appoint such police personnel, including police officers, staff, constables and superior officers, as they deem necessary and to fix such persons’ compensation. The commissioners shall make and enforce all rules necessary for the operation of the police force in the manner most beneficial to the public interest. The commissioners may at any time remove police personnel for just cause and after a hearing satisfying the requirements of due process, which cause shall be specified in an order of removal except that special police officers appointed and designated as such shall serve at the pleasure of the commission and may be removed for other than just cause.