Unlock duck coop (4)
I believe the answer is:
open
'unlock' is the definition.
(I've seen this before)
'duck coop' is the wordplay.
'duck' becomes 'o'.
'coop' becomes 'pen' (I've seen this before).
'o'+'pen'='OPEN'
(Other definitions for open that I've seen before include "ready to entertain new ideas" , "Willing" , "Traditional room heater" , "Overt" , "Not closed or obstructed" .)