You should never anchor from the stern. The exception to the rule being if you have an anchor set from the bow, and you want to keep the stern from swinging around, like when fishing over structure. I use 2 anchors when I fish for sheepshead at the jetties. However, keep the stern anchor on some kind of heavy duty snap, where you can detach it in a hurry if need be, or keep a knife handy to cut the rope if you get into trouble.
Also, because I fish around rocks and I'm using danforth anchors which dig in and hold position, I use a small fender float on my stern anchor line, so I can detach it, pull forward and break the bow anchor loose, then come back around and pick up the stern anchor.