I excavated a large section of my concrete basement floor to replace some plumbing. The resulting hole is roughly five feet square, and three feet deep. It is next to one of the foundation walls. About two feet of the dirt below the footing is visible. I would like to keep this "hole" accessible for future renovations. What is the best way to go about building a retaining wall (for the visible dirt below the footing)? Would you recommend a cinder block for the job? If so, would 8x12x4" blocks work, or should I go with the standard 8x12x12 blocks? Or, should I just hire a mason to form and pour something? Thank you!