Heh, rock stacking... the cardinal sin of 4-wheeling. Screw that. If I'm in a jam I'll be grabbing rocks left and right. In a battle between $$$ repairs of some quaint notion of trail "purity," my pocketbook will win every time. It's not like a 4x4 competition where I'll lose points for stacking!
Stacking has its place when safe passage is essential but I will admit it's often a substitute for lack of skills or wheelers with no balls. Or people who have no business on a trail. In any case, I think the basic 4-wheeler ethos must include a good dose of common sense and making sure things are unstacked afterwards. That's really the key.
Firebird and Lower Scorpion will be a challenge and we'll see what happens.