Cosmetic watch-dog? (9)
I believe the answer is:
eyeshadow
'cosmetic' is the definition.
(eyeshadow is a kind of cosmetic)
'watch-dog?' is the wordplay.
'watch' becomes 'eye' (I've seen this before).
'dog?' becomes 'shadow' (dogging is a kind of shadowing**).
'eye'+'shadow'='EYESHADOW'
(Other definitions for eyeshadow that I've seen before include "used to put dark side into orbit" , "beauty aid" , "application to viewers" , "part of make-up" , "Face application" .)