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've got four of these at my base and I've got way too much cementing paste so take note four is enough, but you probably also heard that they produce organic polymer which acts the exact same way as regular polymer except for having a spoil timer which is it's downfall. These don't produce very large quantities of this material however if you have a lot of it and you don't want it to spoil, turns out you can add it to their inventories on top of what they naturally produce and they will triple it's time left as an item - which works perfectly alongside something like a kairuku farm.
Hope that helps some of you, this gives me so much more time to get more polymer now and it even makes converting it to regular polymer through demolishing structures inefficient :)