Seems like I remember from the distant past that you would buy a small skin patch and then use hide glue to attach it to the inside of the head. You could get it done at a musical instrument shop. I also seem to remember that a clothes iron was involved too, to flatten the patch and cure the glue. It didn't smell very nice either, but would go away after it dried. When the patch would get wet it would smell bad again for awhile. Bass drum heads commonly had multiple patches because they were expensive. I remember the patches were in a distinctive oval shape and they came in different sizes. I guess I am showing my age here.