Walls help?

I want to make cliffs that can be lowered by a trigger. I make some sort of a castle wall from cliffs and when a doodad on it is destroyed I want the cliff to be removed (lowered). How do I do that?

You can't. You might try instead raising the terrain and using the plateau tool to create walls. Don't forget pating blockers. Then, for your trigger's actions, create negative craters along the wall. Not sure how well this will work though. Also, you'd need to remove the pathing blockers.