If your zoom creep problem is solely when walking around with your camera rather than in shooting vertically , then using a camera strap that attaches to the tripod screw may help. They are especially useful for larger lenses that have a tripod collar. Attaching the strap to the foot brings the outfit more into balance allowing it to hang horizontally. This also reduces strain on the lens to camera mounting point.
Black Rapid is the best known brand but there are much cheaper imitations that do the job equally well.
http://www.blackrapid.com/