Re: Cat Safety Collars
Both of our (indoor-only) cats wear safety collars. Desdemona's had hers on for two years, no breakage. Last summer, I came home one day to see a collarless Othello. We were baffled about what could have happened to his collar, and finally went and got him a new collar and tag. A month or two later, we went to use the sewing machine for the first time in a while, and there it was - Othello must have been poking and rubbing around the underside of the sewing machine table and gotten his collar caught, and the clasp broke away, just the way it's supposed to. So, I'd say safety collars work.
You might want to consider getting your free-roaming kitties microchipped, too - the collar is a nice visible form of ID, but a microchip can't come off or get lost, so the combination of the two is probably a good idea.