Staples in my town is selling rubber wristbands to support the American Cancer Society. They are offered in several colors, including black. I made my $2.00 donation and got one of the black ones, which fits very nicely around the barrel of the 70-300 IS, spanning the joint between the lens barrel and the back of the zoom ring. It is unobtrusive, applies enough extra friction to the rotating joint to keep it from turning under the weight of the zooming portion of the lens, and the tension can be varied by adjusting the amount of overlap on the zoom ring.