This seems to be one of the alternatives: Opteka Tripod Collar


I use the 70-200/4L IS with a genuine Canon tripod collar. It locks the lens pretty solid and it gives me a good sense of security when used on anything (lock solid on tripod head vs rotate frequently on my monopod). I personally haven't tried any 3rd party rings, they may turns out to be as usable but once if something goes wrong you're putting your lens along with the camera body at risk. The tripod ring is rather delicate so you may want to get one with good strength.


my $0.02