Or our dogs only Jake has a collar on all the time. The reason being he can jump the fence. He rarely jumps, in fact the only times he has gone over has been when we've been on the outside of their 'dog potty yard'. Nonetheless we keep keep a collar on him all the time just in case. The other dogs only wear collars when we leave the yard.

Of our cats only Sundae wears a collar. She's been known to be a bit flighty in the past. It's been a long time since she's tried to escape, but I feel better keeping a collar on her anyway.