My grill guard is made stout enough, using 3/8 and 1/2 inch plate with 1/4 square tubing, but it will only take some of the load of a direct hit. It may save some of the components but, from the deer I have hit I know it won't take it all. I wiped out my wife's Dakota a few years ago to the tune of 8 thousand. A grill guard wouldn't have done much. I don't have any experience with deer whistles, but if they worked I would think that they might have become standard equipment.
Dave