Animal quarters (4)
(Other definitions for hind that I've seen before include "Female animal; at the back" , "posterior" , "Female red deer" , "Rear - female deer" , "Be much better than (someone)" .)
'animal quarters' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for pens that I've seen before include "Literary thought or reflection" , "birds" , "Dashes off" , "Female swans" , "Writing implements" .)