I'll agree that a pipe wrench is likely to severely mar the finish, as you'll probably have to reposition it a number of times. What I have used to remove rebar that's been pounded into the ground* is a pair of vise grips. Lock 'em on properly, and they only make one set of tooth marks. Then you can use them to apply torque in either direction. Once you have the bar rotating, you can also use the vise grips to apply upward pressure.
*Here in Arizona, the ground is so hard that election signs can't be held up by wooden posts. They all use ⅜" or ½" rebar. I'll sometimes go out after the election is over and pick up a free load of corroplast and renew my supply of rebar. Not only is it free, but it's also a public service - by law, election signs must be removed after elections.