I've got a bunch of cat litter buckets. I figure on sticking the tree in with a cross piece in the trunk. Then screwing some pallet lumber in an "X" across the bottom with long deck screws so it always stands up and then putting half a bag of quickrete in it, that's 40 pounds. Then I'll fill the bucket the rest of the way up with large limestone. That should sink a 7 foot Christmas tree I'd think. They will go on the ice in position. Our ice doesn't tend to drift.