I'm taking a secret from your "secret garden" Cathy. In one of the pictures I posted, I was showing the flowerbed on the west side of our house. To form that bed, I used a radial arm saw and cut up probably 50 landscaping timbers, dug a trench around 1 foot deep and buried the cut timbers (each around 18" long) in the trench standing them up on their ends and butting them together side by side. A lot of work. And if you look at the picture, you'll see that they have rotted even though they were treated.
I need to pull all of those out and I think I'll use those chunky stone type borders that you used in those first and second shots of the rockwork you posted. I don't think the stone will "rot" <LOL>.
I have those timbers ALL OVER the yard, around trees and on three sides of our house. The timbers looked good, like stockades, but it isn't any good if they don't stand up to the test of time!