Use the fender washers to hold on the edges . This maintains the integrity of the entire sheet. Buy Lexon it is pretty "Bullet-Proof" in any thick or thin dimension. I have had a large window of it getting beat on now for 15? years being OPEN every night of the year. A local Hot Rodder ordered it originally for the side windows of his car but never picked it up at the hardware store.
If the piece is large enough and someone hits it hard enough it may flex enough to leave it's frame but it will not break, so make a deeper frame for it to keep it where you need it.
I was told about a house that put Lexon over an entire doorway that had their 200 pound+ "Werewolf" run down the hall and jump at customers as they walked passed the doorway, he would hit it as if being stopped mid-air and be thrown back, it never broke. Learning to fall back safely on the werewolf/actor's part was the trick.