Removing Under Coating?

This isn't PC and probably violates a ton of EPA regs, but you asked for techniques that work. This one does.

Back in the day, we used to prep bodies retrieved from salvage yards by stripping them completely. To get rid of the undercoating and other junk on the underside, we would get a case of beer and a couple of gallons of diesel fuel. We'd roll the car over on the roof and douse the underside with the diesel fuel and light it. The beer had two purposes; something to do while watching the burn and a portable supply of water to put out any un-intentend fires. We'd still have to use a wire wheel a little bit after things cooled.

The scariest thing we had happen was a rear quarter panel fell off a Fairlane once while the burn was on. Evidently undercoating doubled as an adhesive on the particular day at the factory.