Before authorizing any expense in accordance with section 7D.29, the executive council shall, in each case, by resolution, entered upon its records, set forth the necessity for authorizing such expense, the special fitness of the one employed to perform such work, the definite rate of compensation or salary allowed, and the total amount of money that may be expended. Compensation or salary for personal services in such cases must be determined by unanimous vote of all members of the council.