Mine did not come off my neck from 1967 - 1992 (except to replace the silencer tubing that always dried out and got too hard) when I retired. They still go back on when I go out with Scouts Camping. That plus the set on my key chain and the one laced into my running shoe.
When I worked at jumpmaster branch the day of actions in the aircraft testing all students had to have ID card & dogtags or they failed the entire course. During the inspection one of the marines didn't have his dogtags and looked like he would be going home. Right at that time one of his fellow marines said check your boots and sure enough there was dogtag secured with a bootlace on each boot.