Changes of pull on an anchor, by tidal forces or wind shift, can flip the anchor out of the bottom. Full chain, or a kellet (weight) may prevent nasty consequences, but for longer stays I prefer 'bahamian'. I.e. two anchors opposite each other with the rode or warp from the boat exerting forces on the grouns tackle in between both anchors. Various alternatives to this 'bahamian moor' are practised..
My particular approach on 39' Zeewind consists of a primary Fortress 37 anchor on a chainlead plus nylon rode. It is dropped the usual way, but on twice the scope. After reversing to set the anchor, my secondary Fortress 23 anchor (with rode equally prepared) is dropped from the stern, then leading the rode forward outside the rig.
At the bitter end of the rode a snatchblock is connected, which I clip over the primary rode outside the bow. After the scope of the primary rode is brought back to normal, this block rides up and down the primary rode avoiding chafe. This because of the dynamic changes in direction and pull of the boat.swinging round on it single warp. All the time, whatever the direction and pull, the anchors are drawn together with the only effect being to dig in better.
