Here's one idea: Amazon.com : Quiet Spot Pet Tag Silencer (Black) : Pet Identification Tags : Pet Supplies
I don't keep the rabies tags or dangling ID tags on my dogs' collars because they always seem to get pulled off and lost. Yes, I'm supposed to keep rabies tags and the county license tag on their collars but never have and have not had an issue with that. I use boomerang tags for ID, you could get the microchip number engraved on one of those tags, some allow engraving front and back. Boomerang Tags