A Steel bumper is probably your best choice. That way when you use it as a slider off those steep drops in Sedona its OK to scrap, a little scraping does not matter. Moving to 16" rims and taller side wall tires would help you too...Like 275/70/16's. You can also lower your air pressure for more grip and not loose much ground clearance with 16's. I had those 18" rims on my Discovery when I first got it. They are really for soccer moms and highway driving Another option would be to put your spare in your back temporarily, it would take the weight off your rear door.

Now I really want to go to Sedona to wheel and mountain bike. Your making me jealous.