Thomas Kendrick wrote in
:

Pulling the post depends on what is to follow.
I had a neighbor try to pull some wood 4x4 posts which must
have had 2
bags of concrete mix per hole. He wanted to replace the fence
with a
brick retaining wall. Borrowed my pair of farm jacks - all it
did was
break the posts off at ground level.
I recommended that he break them all off at ground level and
rent an
electric jackhammer to break the base up if he really needed
the
concrete removed.

In a similar situation, I just dug down to the concrete (about
6" below surface) and cut the posts off with the sawzall. Filled
in the holes and forgot about the concrete.

-drl