Such a dog may be put down as hairy (9)
I believe the answer is:
dangerous
This clue is a double definition.
'such a dog may be put down' is the first definition.
(a dangerous dog might be put down)
'hairy' is the second definition.
(thesaurus)
'as' is the link.
(Other definitions for dangerous that I've seen before include "Hazardous" , "Not safe" , "Insecure" , "Harmful, injurious" , "Unsafe, risky" .)