A simple fence that discourages snails and slugs - it's hard to slide over, faces outwards and interrupts the natural 'shortest path' to the food. Also has spikes on top for last line of discouragement.
The wall is a fence rather than solid so that sunlight can still get to the plant.
This is the improved version of my earlier thing. It now has reinforcing rings that make the print much easier and better, with hundreds of numbs on the rings to discourage the snails even further.