(a) Certificates of indebtedness issued and sold by the Commissioners Court of Dallas County to acquire property and to construct, enlarge, furnish, equip, and repair buildings used as homes and schools for delinquent children that have been submitted to the attorney general, approved by the attorney general, and registered by the comptroller are incontestable.
(b) The certificates are legal and authorized investments for:
(1) banks;
(2) savings banks;
(3) trust companies;
(4) savings and loan associations;
(5) insurance companies;
(6) fiduciaries;
(7) trustees;
(8) guardians; and
(9) sinking funds of municipalities, counties, school districts, and other political subdivisions of the state and other public funds of the state and its agencies.
(c) The certificates are eligible to secure deposits of public funds of the state and of municipalities, counties, school districts, and other political subdivisions of the state. The certificates are lawful and sufficient security for deposits to the extent of their market or face value, whichever is less, if accompanied by all unmatured coupons.
(d) The commissioners court shall continue to levy a tax that is sufficient to pay the principal of and interest on the certificates so long as certificates are outstanding.