It's a corking preventative! (7)
I believe the answer is:
stopper
'corking preventative' is the definition.
The definition and answer can be both man-made objects as well as being singular nouns.
Maybe there's an association between them I don't understand?
'it's a' is the wordplay.
'it's' becomes 'stop' (I can't justify this - if you can you should give a lot more credence to this answer).
'a' becomes 'per' (eg 'one a day' means 'one per day').
'stop'+'per'='STOPPER'
Can you help me to learn more?
(Other definitions for stopper that I've seen before include "Maybe cork" , "Cork - goalkeeper?" , "Perhaps cork" , "Plug for a bottle" , "Bung" .)