Several years ago we made an Alaska trip in a caravan. One of our companions had a DP similar in size to ours with a solid, $500 "Zephyr" Board as a rock guard. Our rig had a $100 Camping World "Rock Solid" guard that has multiple heavy plastic strips behind the rear wheels. We both towed Jeeps and traveled the same roads together at the same speeds. At the end of a day of rough roads, our toad was covered with road dust but no rocks. Our companion's jeeps hood and roof were covered with rocks. His guard acted as a big scraper and stirred up the rocks.