Leg press, deadlifts, RDLs, lunges, leg extensions, leg curls, hack squats, split squats. All those will hit your legs, plus there variations. Do some sprints, run hills, stairs, those will hit your legs. Im sure there are more lifts I can't think of this second as well.
While natural gas occurs in nature as a mixture of methane and other gases, propane is actually a byproduct of both petroleum refining and natural gas processing.
A natural gas BBQ is cheaper to run than a propane BBQ and it is more convenient to use. With a propane grill, you have to make sure you have propane cylinders on hand or you may sometimes find that you have prepared food but can't cook it.