Canadian policeman could be free after a second (7)
I believe the answer is:
mountie
'canadian policeman' is the definition.
(the Royal Canadian Mounted Police are the Mounties)
'free after a second' is the wordplay.
'free' becomes 'untie' (I've seen this before).
'after' means one lot of letters go next to another.
'a second' becomes 'mo' (both are short periods of time).
'untie' after 'mo' is 'MOUNTIE'.
'could be' is the link.
(Other definitions for mountie that I've seen before include "One policeman" , "Canadian cop on a horse?" , "Member of the Royal Canadian Mounted Police" , "North American policeman" , "Horse-riding Canadian cop" .)