Gun dog bounds off, free (4)
I believe the answer is:
undo
'free' is the definition.
(as in undoing someone's chains)
'gun dog bounds off' is the wordplay.
'bounds off' says the answer is hidden in the clue (the answer is bounded or enclosed by the clue).
'UNDO' is hidden within 'gun dog'.
(Other definitions for undo that I've seen before include "Ruin or loosen ties" , "Cause downfall" , "(4)" , "Open buttons or ruin" , "Ruin or undermine" .)