Pet in front of a barrier heard to yowl (9)
I believe the answer is:
caterwaul
'yowl' is the definition.
(I've seen this before)
'pet in front of a barrier heard' is the wordplay.
I cannot really see how this works, but
'pet' could be 'cat' (I have seen 'Common pet ' mean 'cat' so perhaps 'pet' could also mean 'cat') and 'cat' is present in the answer.
'a' is present in the answer.
This explanation may well be incorrect...
'to' acts as a link.
(Other definitions for caterwaul that I've seen before include "queen's complaint" , "Make feline howl about curate law" , "Feline shriek - cult aware (anag)" , "Wail or howl shrilly" , "howl unpleasantly" .)