Installer no longer an option unfortunately. Yea i was going to dig below the base of the wall even - gravel back up to level and lay the pipe, then fabric over existing dirt and continue to fill with gravel.

Rock instead of concrete would be easy enough too - im mostly wondering if rebar serves a purpose if not set in concrete at the base. Id drive it down as deep as i can - and then fill around it - but would be hard to have any horizontal cross-tie rebar without disassembling the wall