Conventional poster close to fine wooden barrier (8)
I believe the answer is:
stockade
'wooden barrier' is the definition.
(I've seen this before)
'conventional poster close to fine' is the wordplay.
'conventional' becomes 'stock' (as in stock phrases).
'poster' becomes 'ad' (short for advert).
'close to' suggests the final letters (the close of something is the end).
The last letter of 'fine' is 'e'.
'stock'+'ad'+'e'='STOCKADE'
(Other definitions for stockade that I've seen before include "Wooden barrier" , "Defence barrier" , "defensive structure" , "Protective fence of upright stakes" , "Staked barrier" .)