My mother had one of those on her bed with the elastic running around the top of the edge. It kept slipping under the top mattress every time she went to change her sheets. As she's 86 now, the top mattress is too heavy for her to lift to retrieve the skirt. I'm making her a new one from an old one I had for the spare bedroom. I'm using an old bottom sheet, marked for velcros. I separated each side (3) so all she has to do it remove the side that needs washed. Plus having it in 3 pieces keeps them from twisting so much in the washer. Just my take on it.
Suz in Iowa