boshaw wrote:vclaim under your minehole
wall in cave system matching them at the edges of your walls on the surface
Walls can be built in caves, but not flush against the sides of the cave. (walls do work flush in mined sections.) A claim alone doesn't stop raiders and you can't completely "wall" your section of the underground off. Someone can still dig into the parts that aren't walled.
sabinati wrote:why
For the first idea, the same reason why it wouldn't be good to give everyone in your village the ability to build crossroads or take signs from them. For the second, because it's a non-ram method of crossing a brick wall.