La. Stat. tit. 17 § 2188
Bonds, notes or certificates of indebtedness issued hereunder shall not be invalid for any irregularity or defect in the proceedings for the issuance and sale thereof, and shall be incontestable in the hands of bona fide purchasers or holders for value. The provisions of the resolution authorizing the issuance of said bonds, notes, or certificates of indebtedness shall create a valid contract between the board of supervisors and each and every holder of said bonds, and the provisions of such contract shall be enforceable by appropriate proceedings to be taken by such holder or holders either at law or in equity. The said bonds, notes, or certificates of indebtedness shall be a valid obligation of the board of supervisors in favor of any holder for value, and no court shall enjoin the payment of the principal or interest thereof, or the setting aside of the revenues pledged to the payment thereof.
La. R.S. § 17:2188