Boulders

[Repton]

Idea: use a pick axe to hack a boulder out of a wall. Takes a few turns, chance of failure (resulting in a hole in the wall but no boulder).

Boulders would be like boulders in nethack. So you can push them around, you can't move through them, and they block line-of-sight.

[Final Master]

So a non magical permanent stone wall? I... am not so sure. The classes that really need a means of los disruption would really rather phase away.