Have you got a neighbor you don't like? Park the truck so the runoff drains his direction! I use a strong solution of Trisodium Phosphate, mixed with water to form a thin paste and applied with a brush. Let it soak a couple of days and hit it with a pressure washer. TSP powder is sold at big box hardware stores like Home Depot as concrete driveway cleaner. Isn't phosphate a major component of fertilizer? It might actually help the grass grow!

I've also immersed engine blocks and heads in a 55 gallon drum of water sitting on a couple of concrete blocks with a box of Tide laundry powder and 2 cans of lye dissolved in the water and built a fire under the barrel. After a day of boiling, the parts were clean down to bare cast iron!
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!