Half-dead barriers provide protection (8)
I believe the answer is:
defences
'protection' is the definition.
(I've seen this before)
'half-dead barriers' is the wordplay.
'half' means to take half the letters.
'barriers' becomes 'fences' (fence is a kind of barrier).
'dead' with half the letters taken is 'de'.
'de'+'fences'='DEFENCES'
'provide' is the link.
(Other definitions for defences that I've seen before include "barricades" , "legal cases for those charged" , "Means of protection" , "Protections or justifications" , "ramparts?" .)