Never place the LR on glass. Why? Because it could slip in the future and break the glass. Second it will scratch the tank making it weaker. you should place the LR wider at the bottom and slowly go inward like a small rock pile. If placed right your rocks will never move. Snug them in there just right and you'll be fine. I have a 75 gal set up with about 130# of LR without touching the glass. Been set up that way for a couple of years now with no problems.