I anchored last month up in the Northeast Corner near the prohibited zone in about 20 feet of water. We found good holding!
Had a guy drag anchor next to me, no one was on the boat. Besides not setting his anchor properly I think he was on that 12' mound, then when he dragged off of it..his anchor was just hanging. Tow boat came an took him to a mooring.
Best you can do is make sure you get a good set, watch the other vessels around you and see how much scope they have out. We were all fine on Friday..by Saturday afternoon that corner starting filling in. Had a boat that was sitting almost directly over our anchor when we went to leave early sun morning, managed to retrieve it in a wind shift, without having to ask them to move.