Do like to put in some defensive work (7)
I believe the answer is:
parapet
'defensive work' is the definition.
'do like to put in some' is the wordplay.
'do like' becomes 'ape' (both can mean to imitate).
'to put in' is an insertion indicator.
'some' becomes 'part'.
'ape' going inside 'part' is 'PARAPET'.
(Other definitions for parapet that I've seen before include "wall, protective one" , "balustrade" , "Low protective wall along edge of roof or bridge" , "Low wall along the side of a bridge" , "Defensive line" .)