Quick look as dog is heard (4)
I believe the answer is:
peek
'quick look' is the definition.
(I've seen this in another clue)
'dog is heard' is the wordplay.
'dog' becomes 'peke' (short for Pekingese).
'is heard' indicates a 'sounds like' (homophone) clue.
'peke' sounds like 'PEEK'.
'as' acts as a link.
(Other definitions for peek that I've seen before include "Quick or furtive look" , "Quick, sly look" , "Furtive glance" , "Glimpse" , "Sly look, peep" .)