"There is a commercial available product called Rip Rap made by a few concrete manufactures (the 4th image in the post features it). It's only used for erosion control. It's application is not intended for use for building foundations, structural or freestanding walls. When using the correct product for the correct application (not the standard concrete shown in most of these photos) this is a great solution for building small scale retaining walls.A little reference for you all.  https://www.quikrete.com/pdfs/data_sheet-rip%20rap%201129-60%20-61%20-62%20-80%201134-80.pdf"