The phrase "haddest a lock on" means to have complete control or monopoly over something. Its antonyms can be words like relinquish, surrender, yield, give up, abandon, and let go. These words imply the act of releasing control over something, allowing others to have equal opportunities to access or enjoy it. Another set of antonyms for "haddest a lock on" could be share, distribute, divide, and apportion. These words suggest the idea of splitting or sharing the control or monopoly over something with others. In any case, the antonyms of "haddest a lock on" are words that promote fairness, equal access, and sharing of power.