Protection against half-dead barriers (8)
I believe the answer is:
defences
'protection' is the definition.
(I've seen this before)
'against half-dead barriers' is the wordplay.
'against' says to put letters next to each other.
'half' indicates taking half.
'barriers' becomes 'fences' (fence is a kind of barrier).
'dead' cut in half is 'de'.
'de'+'fences' is 'DEFENCES'.
(Other definitions for defences that I've seen before include "ramparts?" , "Means of protection" , "legal cases for those charged" , "Protections or justifications" , "barricades" .)