Here's an idea...
build a 'curb' out of old ties, maybe two courses high, pegged through with long rebar, along the turntable's swing, around to both ring wall ends.
It will--
*block driving or working in the 'table's working area.
*keep dirt from washing into the 'pit'.
*maybe satisfy those who want to see an un-needed, full ring wall.
*look cool.