Depending on how bad the stains are, but if BAD, I use carburetor parts dip. Keep the spot wet for an hour or so, then take a stiff steel wire brush, and scrub as hard as you can. Reapply the sauce, and do it again an hour later. Get the "good stuff" carb dip, like Berrymans Professional. That stuff sinks really BAD, so be warned. It cleans well though. When done, you will have a bleached white spot on your driveway where the grease was. No waterbased citrus or similar cleaner comes close.