In order to assure employees the fullest freedom in exercising the rights guaranteed by this law consistent with the joint responsibilities of both the employer and the employees to serve the public, the Director shall decide an appropriate unit for the purposes of collective bargaining in each case where certification is sought. In determining an appropriate unit, the Director shall take into consideration, but shall not be limited to, the following: Community of interest; The history of collective bargaining; The desires of the employees; The effectiveness and efficiency of labor management relations affected by the unit; and The effects of over fragmentation and the effects on the efficiency of government operations. The Director shall not decide any unit is appropriate if such unit includes both supervisors and non-supervisors, or such unit includes both professional and nonprofessional employees, unless a majority of such professional employees vote for inclusion therein. Supervisors or professionals may be permitted to form their own separate homogenous units. This Section shall not be deemed to preclude multiunit bargaining. Arbitration regarding appropriate representation units. Whenever the Director and the petitioning labor organization are in disagreement as to the determination of the appropriate representation unit, the issue shall be submitted to arbitration at the request of either party. If the parties are unable to agree on an arbitrator within five days of the initial request, they shall make their selection from a list of five neutrals submitted by the American Arbitration Association. If the parties are unable to agree on the selection of one of the arbitrators within three workdays after receipt of the list, the County and the labor organization shall strike one name from the list alternately until one name remains. The remaining person shall be the arbitrator. If the selected arbitrator is unable to serve, the arbitrator shall be appointed directly by the American Arbitration Association from the panel list originally submitted. An arbitrator shall render a decision within 30 days after appointment unless the parties mutually agree otherwise. The arbitrator's decision shall not be subject to court review, except with respect to unit determinations that are alleged to be contrary to law. The cost of obtaining the panel and the fees and expenses of arbitration shall be borne by the County.