Easy way to keep them in place, just fill their inventory with stone. Encumbered, they will not move, even on wander. Then for feeding, put cake in a tough. They will stay in place and alive! Making you resources the whole time... Up to the top for knowledge!
TIPP: Achatinas can produce organic Polymer. You can just craft a fridge with the organic Polymer and destroy it. Every time you destroy a fridge you get normal Polymer back. That means you can transform organic Polymer to normal Polymer. I found it out yesterday by myself.
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.
I have 10 of these and never have a issue with paste... ever. I have flown 3 argies full of obsidian back to base and ran out of that before the paste. Also makes repairing gillie suit so much easier. Any time it breaks I run to the snail shed and have enough organic poly to repair pretty much anything.