Release of gun dogs (4)
I believe the answer is:
undo
'release' is the definition.
(I've seen this before)
'of gun dogs' is the wordplay.
'of' indicates a hidden word.
'UNDO' is hidden in the letters of 'gun dogs'.
(Other definitions for undo that I've seen before include "Cancel -- annul -- reverse" , "Subvert" , "Cancel, annul; open" , "Ruin, destroy" , "Open or unfasten" .)