Cut both legs off an old pair of panty hose at the bottom of the panty part.
Tie a knot in each toe end of the leg parts to reinforce them to make roof socks.
Lay the legs out on a hard work surface. Have an assistant open the top of the first panty hose leg and hold it open.
Slowly fill the leg part with calcium chloride ice melter until it's within a couple of inches of the top.
Grab the top of the pantyhose leg securely and close it with a tight knot to make a roof sock. Fill and secure the second leg.
Place the socks on the roof a few feet apart so they cross over the ice dam and across the gutter, or a few inches over the edge. Use a long-handled rake if necessary to push them into place. The calcium chloride will melt the ice dam and create a furrow. The water will flow either into the gutter or off the edge of the roof.