Your concrete panels are a great idea! I was wondering if you could detail a bit just how you built them. I assume you used forms. Did you build your own forms? Did you make multiple forms so you could make multiple panels all at once? Also, how thick are the panels? From the pictures I would guess 2" (or really a single 2x piece of lumber width). Is this about correct?
There is a youtube site "Man About Tools". I paid for the 4th version of the digital drawings for these forms and modified them slightly. In "DIY Simple Concrete Garden Box - PART 1 - Make the Forms" he describes these boxes and he sells the digital plans on a link under the youtube window.
https://manabouttools.com/concrete-garden-box-panels-version-iv-digital-plan/
Other people may reject you but if you lie in the forest floor for long enough the moss and fungi will accept you as one of their own!