17-5-923. Trust indenture. In the discretion of the board, bonds issued under this part may be secured by a trust indenture by and between the board and a trustee, which may be any trust company or bank having the powers of a trust company inside or outside of the state. Each trust indenture or an executed counterpart thereof must be filed in the office of the secretary of state. The filing of a trust indenture or an executed counterpart thereof in the office of the county clerk and recorder of the county in which the property covered by the trust indenture is located is constructive notice of its content to all persons from the time of filing, and the recording of the trust indenture or its content is not necessary.