Dry walls can be made of broken concrete, old tires(makes a great retaining wall to protect the 1964 Chevy pickup on blocks, behind the chicken coop) , logs(don't last long), concrete block (what's the point?), rocks, railroad ties (see logs) and almost anything else you can stack...
Interestingly, small gardens can especially benefit from defining discrete garden “rooms” using edging; most landscape designers know that dividing any space into a few smaller spaces makes the overall area appear larger. This is achieved partly due to the element of surprise and discovery: “Wher...