This thread in enlightening as an ag producer. I know not everyone has the same background in agricultural pesticides as we do, but I expected more knowledge from this group. Yes glyphosate(roundup) is a non selective broad spectrum herbicide that will kill most plants, but it is strongest on grasses, there are much better broadleaf herbicides. I actually think what you want to accomplish would be to get rid of the broadleaf weeds and leave the short grasses. 24d or dicamba would be a start, but they offer very little residual. If the grasses don't have to compete with the broadleafs, they will eventually take over and it could be a weed free area. Bare soil is rarely sustainable or desirable for that matter. Lastly, you say that maybe you'll leave it up to them??? If you don't own the ground, you better be really careful applying herbicides to someone else's property. Applying ground sterilant products could have long lasting impacts, what if the ground would someday want to be used for another purpose than a rifle range.
And as for the burn injury, I'm very sorry for his health issues, but I have almost 100 percent certainty that that was not caused by 3 hrs of exposure to glyphosate.