Wall Bag (4-Pack) is another great way to help your winter cover stay securely mounted to your above ground pool, making pool re-opening in the Spring much easier. Simply fill them with water and place them on top of your winter cover (along its perimeter) to protect it from high winds that can loosen even the most tightly sealed cover. Made from thick vinyl sheeting, they are designed to handle years of freezing temperatures without splitting or leaking and can be easily filled with a garden hose. Best of all, Water Bags (4-Pack) have built-in grommets to let you connect them to your winter cover cabling, keeping them in place.