We use rocks for borders and wood for raised beds. Natural rocks can also be layered to build higher raised beds, as the Groundswell community greenhouse and garden have done (picture above). Smaller rocks can be used to build a Wicking Bed. Even smaller can be used in pathways; remember that stones or gravel are heavy. More @Wikipedia
Hover over any link to get a description of the article. Please note that search keywords are sometimes hidden within the full article and don't appear in the description or title.