How do I keep the glass top of my coffee table from sliding?

I have this glass cofee table on a metal frame. Problem is, the glass top slides aronund, even though it is heavy. I bought these silicone bumpers, to try to fix the problem, but it didn't do any good. Any hints or products out there that can fix this problem?How do I keep the glass top of my coffee table from sliding?
Have you tried suction cups?How do I keep the glass top of my coffee table from sliding?
they sell little dots that grip the glass
its odd the silicone didn't work is the bottom of the glass dirty have you cleaned it?
Use real silicone from a tube. Apply a dab on the corners of the frame and smooth flat with a wet knife. Let it cure and see if that works.
Just about any hardware store sells these little clear plastic spacers that have adhesive on one side. Sticky side to the base of the table. They work very well....