In the sale of drainage bonds, the directors of the district, if in their judgment it is expedient, may contract with the purchasers of the bonds that the payment for the bonds may be made in such installments as may be agreed upon between them and the purchasers of the bonds; provided, that the payments of the installments agreed upon, as they mature, are amply secured by safe and solvent bond, made in double the amount of the entire deferred installments, payable to the state of Tennessee, for the use and benefit of the district and those entitled, and conditioned for the faithful payment of the installments, such bond to be approved by the unanimous vote of the board of directors of the district before the bond is accepted. The bond and a copy of the resolution of the board of directors approving them shall, on the order of the county court, be spread of record on the drainage record book, and the approval of the board of directors noted on the bond by the secretary of the board writing the word "approval" and signing "board of directors" by the secretary as secretary, or other equivalent words.
T.C.A. § 69-5-907