La. Stat. tit. 39 § 1172
The certificates shall be issued only when authorized by ordinance or resolution passed by the governing authority issuing them and when certificates have been so authorized the governing authority shall dedicate, set aside and pledge not more than two mills of the tax authorized to them for the payment of the certificates, in principal and interest; and thereafter, to keep the funds derived from the tax separate from other funds of the parish, school board, or municipal corporation, and shall devote the entire proceeds of the tax as pledged, or so much thereof as may be necessary, to the payment of the principal and interest on the certificates.
The fund shall not be drawn upon to the prejudice of the certificates, or interest accruing thereon, by the governing authority issuing the certificates, or by its successors.
La. R.S. § 39:1172