A natural creatures toughness does have a catch, its just more complicated than most Paranormal catches.
Bears and Rhinos have a staggering amount of resistance to physical trauma of all kinds, but this armor doesn't really protect against fire, disease, poison, and suffocation. It doesn't protect the eyes or inside the mouth. So the real question is, how should you price a catch that complex? But no matter how you price the other aspects of the catch, its at least a +2, since prettymuch everyone knows, or could figure out, how to kill a Bear or Rhino.
Someone mentioned that high caliber weapons and explosives would satisfy the catch, but I don't buy that. You can kill a Rhino with a high caliber weapon, but that is solely from the damage overcoming its toughness, not negating it (shooting a Rhino with a Desert Eagle isn't going to do as much damage as shooting a horse with the same gun).