I have been double digging my garden in small sections at a time. I started with 8' X 8' and have increased to 10' X 10' now that I was forced to retire. That does not sound like alot more but it is 64 sq ft vs 100 sq ft. I dig down as far as I can dig, which at my place is 28" to maybe 32" until I hit solid cap stone rock. I had been putting a thick layer of leaf mulch on the bottom to hold water. I had never heard of Hugalculture but was thinking along those same lines. I sifted the rocks out as I back filled putting in 2 cart loads of sifted sub soil then 2 heeping cart loads of leaves. I added a few shovel fulls of lime to each layer of leaves. Last year I decided to do a hugalculture bed as an experiment. I followed the same process of layering the subsoil and leaves after the base of rotting wood chips , then logs, then more wood chips to fill in around the logs. I plant my tomatos each year in that new bed. They grow to over 6' high. Here are some pictures.
You can see that I have alot of rock, definately pick and shovel work
I was only able to go 28" in this section
This shows the area almost backfilled. It ended up about 4" to 6" higher then the rest of the garden. It has already started to sink back down some.
When I sift out the rocks I am using them to extend a level area by my fire ring. I am using the biggest stones to form a retaning wall to hold back the rest. I have extrnded the level area by about 4'. It has been years in the making and the garden is just over 1/2 done at this point.