Steve B wrote:

I have a space between my cabin and the sloping hill behind that is about
three feet wide. I want to put up a retaining wall that will be about four
feet high. Behind that, I will fill in an approximately 3' x 3' x square
root of 27' wedge of fill dirt to come to the top of the wall...

How about tying old tires together with synthetic rope, parallel to the ground?

Nick