I'm convinced there are only two ways to keep people away from a buoy. One, is to use an inflatable or dummy horn mine. Even jetskiers are bright enough to know it might blow up, although they might try to take it home anyway.
The other would be to use a white buoy and just mark it "DANGER - MINE" and explain that as meaning it is MINE and I'm cranky about people touching it.
Or maybe stop down by Mines-R-Us and post the video on YouTube afterwards? (G)