In florida the iron content in wells is very high. Allowing a sprinkler system too flow directly on your new drivway will for sure cause staining. Fortunately there is a product sold at ace hardware stores called "white cap". Mix according to instuctions and the stain will come right off. Rust from a blown radiator is another problem completely. The need to move quick is important here. Tri-sodium phosphate mixed into a paste will sometimes remove the stain completly. Never use Muriatic acid...this will make the stain worse and more permanate. Rust stains from fertilizer are the worse. I know of no known remedy to this problem. Perhaps a fist fight with your lawn service would make you feel better. .