The following are the only authorized methods of holding securities:
(1) A domestic insurance company may hold securities in definitive certificates;
(2) A domestic insurance company may, pursuant to an agreement, designate a custodian through which it can transact and maintain book-entry securities on behalf of the insurance company; or
(3) A domestic insurance company may, pursuant to an agreement, participate in depository systems of clearing corporations directly or through a custodian .