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!
Achatina taming generally requires one cake for every five levels, meaning if you want to be resource-conserving, you may want to consider taming a lower level one as opposed to high levels. They also reduce the spoil of organic polymer by 50%, acting as a natural refrigerator for it. It will not last forever, but it does increase its shelf-life. It only ever eats cakes, and nothing else. Bit of a PiTA in that regard but food drain is slow and by the time its hungry you should have more cakes, depending on where you are in terms of gameplay.
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.