AshDVS Normal pop rivet gun? I used normal pop rivets to re-fasten an inner guard in once before. I thought about using scrivets like you find on many local Ford and GM products. Easy to fit and remove. I havent tried to compare sizes though.
K3FSAR I found some scrivets at my local fastner shop that fitted snug. I think I've got one or two left over at home. I'll get some measurements tonight (I didn't want to pop rivet everything back on since I am taking the bumper off in a month or two to repair and respray).
AshDVS good move, I think. Most of the time they're reusable, but if you don't want to reuse, they're easy to remove with sidecutters, etc.