Beleive the old BCARs actually required sufficient fuselage & wing plank thickness that a wheels-up wouldn't start a fire. I remember seeing a mod to add a skid plate to a certain popular Canadian jet after Cranfield had dragged a representative section around (never added to my knowledge).
It's been demo'd a few times in the Biz Jet world - at least once by the HS-125 and once by a GX after one too many gear horn tests. The latter suffered only scratches on the kevlar fairing with the FTE's comment "I thought it was a bit smoother than normal."