Put loads of stone in its inventory to let it wander without moving. If there is a bit space left for the the paste this works fine and you don’t need a cage.

Be wary of cmment saying they eat berries at 200 hunger it is a lie

Collect its slime for cementing paste!

Only upgrade food so when you fill them up you won’t have to feed them again for a long time.

When tamed, the Achatina can produce Achatina paste, an alternative to cementing paste, passively when on wandering. You could also collect it when they are moving, their paste/slime will be on the ground shaped in a similar feces ball.