My "puppy" is almost 10 months old and almost 90 lbs, and we would find he was constantly loosing his collar when he played with our pitbull terrier. He would kindly bring it back in to me, but we were baffled as to why it kept coming off! I then realized during the wee hours of the morning, his neck is a bigger diameter than his head, so unless i snug the collar up under his jaw line, it will probably come off again. Is this common? Is there a better solution? Right now, he's collarless and tagless because of it, and I'm afraid we will get in trouble for him not having the required tags on him.