These are my custom made Wall Markers I use to replace the black cubes.
They are meant to be double-sided with "Damaged Wall" on the one side and "Destroyed Wall" on the other. I glued them on cardboard.
To keep track of the number of spent Wall markers do not flip or replace a „Damaged Wall“ when the wall is destroyed. Just take another marker from the supply and place it on top of the first with the „Destroyed Wall“ side up.
(also see the in-action pitcure in the images section)