I use mod-podge and some felt and glue them to the bottom of ashtrays.
(click photo to embiggen - opens in new window)
(I never imagined that I would ever get this much mileage out of that cigar review photo which I took for another site...)
If I ever put in a bar counter, I think I might urethane/varnish them into the counter, until that point, I just keep them in ziplock bags and old cigar boxes.