They should wear them, but mine doesn't.
I'm really bad about that kind of thing. Actually, don't even know where they are right now... It really is in Ellie's best interest to not wear a collar or harness unsupervised. I don't like them really tight, and when they are at all lose, she gets her nails and jaw stuck. Being in a collar 24/7 seems really uncomfortable. And come to think about it, I wouldn't sleep with something around my neck, so it wouldn't make sense for me to have my dog do that. Used to, but stopped.