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.
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.