I have to replace some low retaining walls. The wood is easy because its
all rotted away, but I can't get the rebar that held them out. The ground
is shale, and doesn't want to give them up.

Any magical solutions? I thought of an auto jack, but don't see how to grip
the bars.
Driving them in rather than reusing them is a solution, but driving them a
foot into shale is a real chore!