I've used numerous shock cord and rubber rand skirts on countless boats and I know what you mean by a shock corded skirt popping off the sides. It's really irratating but this is not the case with ALL shock corded skirts on ALL boats. As Snowwrestler said and IMO, there are way too many varibles at work here to say that shock cord skirts don't offer as good of a seal. Perhaps shock cords are more sensitive to proper sizing than rubber rands but, a shock cord will stay on and remain dry *IF* it's the correct match.