Our cats are microchipped and that works better than a collar. Of course, they have to be taken to a shelter and have it scanned, but I know it works. None of my present cats will tolerate a collar, they actually fight to get them off, Mac is especially adept at this. I don't want to stress Ming because of his FLUTD tendencies, so, microchips it is. If he's worn one before, he should tolerate one now. Keep trying.