How did they keep snakes in a snake pit?

Yes, for their sense organs - i.e. smell.

There are several meanings for 'snake pit'. This is the most common: Snake pits were a historical means of imposing capital_punishment. Convicts were cast into a deep pit containing venomous snakes....

no the garder might eat the ring

By eating them. The black ones u see are king snakes that feed on other snakes

A Benefit of Living with Snakes. They may, in that they prey on snakes as well as other reptiles, birds, small mammals, eggs, insects, etc. But they do not specifically prey on poisonous snakes....