We excavated down to bed rock. Near the fence that was not too far down; near the raised garden we were down a couple feet.
When they put the utilities in as the neighborhood was developed, they cut a trench into the rock down a couple of feet, put the telephone, cable, and electrical lines in it, filled it partly with sand, and then pushed dirt and rock in to fill it back up. This trench runs about 17 to 19 inches from the fence, and is 6 inches wide. If we figure the fence is 1 inch thick, plus 4x4 posts, then the trench runs about 24 inches from the property line.
The idea is to leave the rock between the fence and the trench, and use it as a base for the cement wall that edges the yard. Once we have that wall in place, we will then excavate the rock on the other side of the trench, to give us plenty of soil depth for the South bed.
So first, we frame up for the concrete, using masonite boards spaced with 1x4's, held in place by sacks of compost and manure.
Then we pour the concrete. This section took 15 bags of 60-pound concrete mix. Removing the framing the next day, we have our cement wall.
With one 80-pound bag of mortar mix, we can put the limestone rocks on top to give a finished look. Experimentally, during the process of mixing concrete, mortar and cleaning up afterwards, we can all see that this holds water.
Now we can fill in the section behind the greenhouse -- we've already removed the rock from this section, and we can work then on removing the rock around the base of our oldest olive tree (without upsetting it).