What the other people have suggested sound like good ideas for pulling a
ground rod. Something that might make it a little bit easier before pulling
them with the chain and jack is to put a pipe wrench on the rod and turn it
in the ground a few times. That way the bond between the dirt and the rod
is broken and it should pull up a little bit easier. In fact, while you are
turning the rod, you might try pulling up on it a little bit at the same
time like you are unscrewing it from the ground.