Tough, like a rhino perhaps (5-7)
I believe the answer is:
thick-skinned
'tough' is the definition.
(I've seen this before)
I cannot understand how the rest of the clue works.
Can you help me to learn more?
(Other definitions for thick-skinned that I've seen before include "Insensitive" , "Indifferent to criticism" , "Not easily hurt, upset" , "Pretty impermeable to criticism" .)