Staff members of the elective County officers, at the level of assistant department head or its equivalent level, shall serve in the unclassified service at the pleasure of the appointing elective County officer and in that elective officer's sole discretion. Except for the offices of Sheriff and District Attorney, qualifications for all staff members in the unclassified service of elective County officers shall be established by the elective County officer and approved by the Board of Supervisors. The persons to be appointed as Undersheriff shall be certified by the California Commission on Peace Officers Standards and Training (POST) and the persons to be appointed as Assistant District Attorney shall be a member in good standing of the State Bar of California. This section shall not apply to the staff of the County Superintendent of Schools.