I've always used a split ring to attach tags to my dogs' collars. The latest dog (a rescued Sato) came with a rabies tag attached to her collar with an S-hook. I didn't think anything of it and added her new name tag to the S-hook and squeezed it shut with pliers. Recently we heard some squealing when she was outside, then silence. After a long search, my husband found her trapped in the shed. She was likely sniffing out mouse nests, and had poked her head into a corner where a thin wire from a spare roll of fencing had gotten snagged on the S-hook. She couldn't move 3 inches and was so freaked that she wasn't moving a muscle or making a sound. It was a real fluke, but I've gone back to split rings forever for safety's sake, for sure :o)