I bought some heavier weight white cotton broadcloth and put that on top of the ironing board cover when I used sizing/starch. (I cut it so it had about a four inch overhang all around and serged the edges
It got nasty, but it was easy to whisk off and put in the wash.
It was also good for protecting the ironing board cover when I had a cat that thought that was the best seat in the house!