This is the best anchor on the market end of discussion. It is expensive, but it is the best.
http://www.quickline.us/stainless-steel-anchors.aspx
I have the 5kg model recommended for boats up to 18' and about 3500lbs, it is the smallest one they make. My boat weighs 10,000-12,000 lbs depending on who and what is on board, and is 37' long. With 6' of 5/16 stainless chain and about 50' of line out it held my boat and my friends full cabin 38 Intrepid in a thunderstorm that came up in the afternoon. Winds had to be 50 mph. Both boats were anchored, we were at the sandbar out by stiltsville, almost everybody who tried to stick out the storm had the anchor pull out including my buddy's anchor on the Intrepid, so my little anchor held my boat and his 15000lb beast without issue in sand and grass. I have also anchored in 115' of water bottom fishing for Mutton Snapper, but with 20' of chain, and it held no problem in 2-3 kt current.
I use to have to do the anchor dance I call it making sure it was hooked up at the sandbar or jumping in and manually set it, now I toss the anchor in toss out a little line cleat it off and I am done, it sets every time perfectly. If I really want it set hard I let some extra line out and back down a little and it digs down into the sand and completely disappears.
I now use my fortress as a stern anchor to keep from swinging around or keep the boat pointed a certain way. It will not grab in the grass, only sand or mud.
