For anyone unfamiliar with double digging this is what you do. You take a fork and loosen the soil down to a depth of 1 foot, dig the soil out and then loosen the soil with the fork down another foot.
In my case, the fork doesn't go in more than an inch or two. So I dug out a trench that was 1 foot by 4 feet and 1 foot deep using my pick ax. I loosened the soil beneath that as deep as I could go. Then I took the pick ax and dug another foot-width pulling it into the first trench and thereby creating a new one. I did this over and over again until I'd done it 16 times and had my 4 ft wide by 16 feet long bed.
I used a piece of plywood to stand on the freshly turned soil so I could reach the next area to be dug. As I went I removed any rock that was bigger than my fist. Some of these would get stuck in the tines of the fork when I was forking up the bottom of the trench.
On an average, I removed 2 to 3 wheel barrows of rocks from each bed. Some of them were small boulders that required a digging bar to pry out of the bed. We have piles of rocks along the fence line where I dumped them.
Over the years I've removed most of the smaller rocks in the process of weeding and digging potatoes and the like and now have pretty rock free soil.
Recently I've discovered that I really hadn't gotten all the rocks. A very industrious mole moved into the main garden and tunneled all through the beds! And wherever there was a mole hill, there was a new pile of rocks for me to haul out of the garden! Of course you could argue that he's getting them from under the grass paths but there's too much evidence to indicate otherwise
Double digging is a magnificent way to prepare garden beds and I would never suggest anyone with my kind of soil do it. If I were starting over today, I'd bring in soil and manure to make raised beds. But 22 years ago there really wasn't the money for that much dirt and I had the energy and enthusiasm to do it.
Every year since I've added two heaping wheel barrows of compost to each bed. In the early years I worked this in with a fork. After I while I decided it wasn't worth it and have just layered it on top of the beds since. They've gotten taller and taller and the soil has gotten richer and richer.
Now I add the compost in the fall and cover the beds with leaves to keep down the weeds and protect the soil from the winter rains. In the early spring I pull off the leaves to plant early crops and heap them on the beds that will get later crops.
When I prepare the later beds I pull the leaves off and use them to mulch my potato patch. By the fall, they've broken down and become compost on that bed.