What could make remote wall rot in fort (8,5)
I believe the answer is:
martello tower
'fort' is the definition.
(martello tower is a kind of fort)
'what could make remote wall rot' is the wordplay.
'what could make' indicates an anagram.
'remote'+'wall'+'rot'='remotewallrot'
'remotewallrot' is an anagram of 'MARTELLO TOWER'.
'in' acts as a link.
(Other definitions for martello tower that I've seen before include "Defensive coastal building" , "Coastal defence building" .)