I bought some Rock Tamers by the company Enkay. They attach to the trailer hitch shank and can be adjusted several ways. Mine hang back of the bumper. They might be back far enough to escape the exhaust flow.
I found them at Cabelas and 4 years ago, they cost $200.00.
They have worked well here in North Idaho---the road dept. uses 3/4 inch "sand" to improve traction in winter. Well, maybe not quite 3/4 inch, but it sounds like it when sand hits the windshield.