You can always use the Redneck anchor (a cinder block), which might hold a bit better than a 10 pound mushroom, and that way if somebody steals it...so what?

I had a bass fisherman steal the mushroom anchor off my home made practice mark when I was taking a break on the beach! He didn't take the mark, just the anchor! <img src="http://www.catsailor.com/forums/images/graemlins/shocked.gif" alt="" />