Defender of Italian wine kept in bond, for the most part (7)
I believe the answer is:
bastion
'defender' is the definition.
(I've seen this before)
'italian wine kept in bond for the most part' is the wordplay.
'italian wine' becomes 'asti' (I've seen this before).
'kept in' is an insertion indicator.
'for the most part' means to remove the last letter.
'bond' with its last letter taken away is 'bon'.
'asti' put within 'bon' is 'BASTION'.
'of' is the link.
(Other definitions for bastion that I've seen before include "A projecting fortification to increase angle of fire" , "that's fortified" , "fortress" , "'Stronghold, citadel (7)'" , "Defence - in boats (anag)" .)