The personnel board shall make or contract with the State Merit System Board or other appropriate agency, for a register of all persons eligible and available for appointment to each class of position in the service of the county, ranked according to ability; it is provided, however, that no examination shall be given and no register kept for positions to be filled by persons designated by the board as common laborers. Veterans shall be given preference in hiring in the same manner as provided by the State of Alabama. Layoffs available for reemployment shall be placed at the head of the proper present and subsequent eligible registers in the inverse order of their terminations. Employees who voluntarily terminate their services may be granted reemployment status upon proper eligible registers under such circumstances and in such manner as may be provided for in the board’s rules and regulations subject, however, to stipulations of this section concerning layoffs. Persons desiring appointment may file applications with the board, and the board from time to time, may conduct examinations to test the ability of such applicants. All qualified applicants shall be examined, and examination shall be public, competitive, subject to limitations specified by the board, and open to all citizens of the United States. Examinations shall be practical in character and shall relate to those matters which test the ability of the person examined to discharge intelligently the duties of the position for which he or she applies. In no case shall an appointment be made from an eligible register which is more than two years old, and no eligible register shall be the result of more than one examination.