Armed guard in foreign sector (6)
I believe the answer is:
escort
'armed guard' is the definition.
(I've seen this before)
'foreign sector' is the wordplay.
'foreign' indicates anagramming the letters (foreign order of the letters).
'sector' with letters rearranged gives 'ESCORT'.
'in' is the link.
(Other definitions for escort that I've seen before include "giving protection" , "Companion for social occasion" , "Go with (someone)" , "Companion (perhaps paid)" , "Accompany - Ford model" .)