How to Build a Retaining Wall. In CA, retaining walls greater than requires a building permit (measured from the bottom of footing). Check with your local jurisdiction for exemptions and design requirements.
How to build a cheap garden rock wall or a simple concrete reinforced retaining wall. If you do not have much money and can't easily fix stuff you probably can still build these simple retaining walls.
How to Build a Retaining Wall With Crossties - DIY