Check out CURB

From sandcastles to dirt-stenciling, Curb is doing advertising naturally. Here's a blurb from their What we Do page:

A natural media company

So what's the twig idea? We want to prove that effective and engaging media can be natural and sustainable. To realize our goal, we have a wealth of operational, media and production expertise in every natural material you can imagine. Whether it’s covering a building in flowers, building an exact replica of Windsor castle out of sand or creating a fully fledged amazonian forest in a city centre we can help advise on any creative brief and deliver it naturally and flawlessly.

Check them out at www.curbmedia.com
Let's do this in South Africa too!