Lockets - i suppose the difference with that though is most of us have met a person called 'Lucy' infact loads, so it counterbalances the dog effect iyswim, probably more people called Lucy than dogs. I wonder how many people we all know called 'Rex' for me i haven't met any at all, you also mentioned you hadn't met any except ds , infact i know people who have steered away from that name simply because of its overuse for dog's.
Try googling it and see what you come up with!