Seriously pour rock into a sock, tie the sock on one end, and toss the sock onto the dams/roof line.
Here's how it works:
You can also try a product like this:
I think Calcium carbonate works better, the little pellettes.
If you have access to your attic, either standing or crawling, if you have a window up there you want to keep the window open all winter long. I know this sounds counter-intuitive, but basically you want the temp in your attic to be as close to the temperature outside, which prevents ice dams from forming. The reason ice dams form is because snow melts from the top of your roof (where it's warm -- heat rises from the house) and then it starts to trickle down as water, and when it reaches the eve, there's less heat, it's cold, and it freezes there. Water then continues to build up forming a dam, and then working it's way *up* your roof under the shingles, melting, and dripping into the house.
If you have windows in your attic you can keep them open all year long, basically. For insulation the technique is to try to prevent the warm air from your livable areas from getting into the attic, but to keep the attic itself the same temperature (or close to it) as outside. You'll always get some melting and ice, that's normal, it's when you have extremes in temperature between the top of the roof and the bottom of it when the dams form and do damage.
Roof raking can help too
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