Is he fixing the hair of the dog? (6)
I believe the answer is:
setter
'the dog?' is the definition.
(setter is a type of dog)
I can't explain the rest of the clue.
Can you help me to learn more?
(Other definitions for setter that I've seen before include "who is giving you problems right now?" , "Dog trained to scent game" , "stream of cattle" , "Hunting dog" , "Jelly, perhaps" .)