I know your frustration, although my gang seems to lose them a little less often - actually they seem to go in waves - not losing any for months, and then constantly losing them.

I agree with Chinadoll, maybe you should try a few different kinds first. Also, could it be that the collars are too loose or too tight?

Are you ever able to locate the missing collars? We put ID tags on ours, and they do actually sometimes come back to us.

Good luck