David wrote: "As you can probably note from the above, it is possible to deploy a stern anchor and not be able to retrieve it if you don't have enough bow rode. So, tread carefully."
True enough. If necessary, tie a fender to the end of the stern anchor line, and drop it over the side. Take care of business at the pointy end, and then go back to recover your fender and the stern anchor attached to it.
On a visit to Cumberland Island (Georgia), after a trip ashore that ran longer than planned, I returned to the dinghy to find the tide ebbing fast, and the boat (a 42' GB) sufficiently aground at anchor that even from the beach I could detect a slight list from shore. (I had set a single plow in 9' of water, but close to the edge of a mud bank). Once back aboard, I decided not to try powering off, owing to the risk of bending a prop that might be touching the mud. Waiting out the tide would have been risky, though, as we were right on the edge of the shallows, listing in the direction of deeper water, and the tide was still falling.
What to do? Working quickly, I used the dinghy to set a stern anchor off to the side in deep water. Next, I led that anchor line through the stern hawse and up to the winch, which I then used to take in the stern anchor line, and to thus "kedge" the stern sideways off the bottom. When I felt sure the stern had swung far enough to leave the the running gear in good water, I started engines, twisted the stern out into the current, and slipped the stern anchor rode (with a fender attached). Then I motored up on the bow anchor, approaching from deeper water, retrieved it with the help of the winch, and finally went back to pick up the stern hook.
My inexperienced mate learned first hand that day, and in high-speed mode, the ancient technique of kedging. Our ladies basked all the while on the forward cabin trunk, seemingly oblivious to our little drama.