Dont use a pvc damp course, wall topples at this weak point. Better using a course of engineering brick.
Oooh ! Ready made modular brick walls for quick assembly. 13 inch too ! Where can I buy some ?
Our old garden wall was built like that, it wobbled alarmingly if you nudged it. I just pushed over when I got rid of it for the rebuild.
if that happens just with a wall just imagine what it does to something much bigger