Oh, my! I have never had a design wall to speak of...just a hunk of
flannel taped to the wall. Now I am making a larger quilt for my DD
and needed more space to play around with the blocks. So I raided the
linen closet, found a flannel sheet and pressed DH into service.

He whacked the sheet up on the spare bedroom wall with a few brads and,
voila!, I have a home-made, but workable design wall.
If it falls down...well, I'll move on to Plan B!