How important is a rock shield when towing a car?

We've towed our Jeep Liberty to Alaska and have full-timed with it for 10 years including boondocking along gravel roads. We have had no damage to the Jeep from rocks.

One other thing, we have stiff flaps behind the MH wheels but we don't have a rear stiff flap. We actually saw folks along our Alaskan trip removing those stiff across-the-rear flaps because of rocks laying at the base of the toad's windshield.