Since the series is canceled, I've thought I can give my idea for a new member I just came up with.
Anubis - A black pharaoh hound who has been reassign as the newest member of Shelter 17. He is a real mystery, acting quiet, shifty and tranquil. His specialty is stealth and infiltration. Blending into shadows and sneaking into infiltration locations undetected. Anubis is a talented spy, thief, and delivery dog. He was very distant from the other Pound Puppies, but they soon begin warming up to each other.
Osiris - A black oriental cat who was reassign to Happy Valley Shelter 71 as part of the Kennel Kittens. Just as mysterious as Anubis. Not only is Osiris his cat counterpart, but they have been rivals for quite some time. His abilities in stealth and espionage are a match for that of Anubis's talents.