Sounds like Cologne is popular with the foreign guard (8)
I believe the answer is:
sentinel
'guard' is the definition.
(I know that security guard is a type of guard\nI know that lookout is a type of security guard\nTherefore, lookout is a type of guard)
'sounds like cologne is popular with the foreign' is the wordplay.
'sounds like' indicates a 'sounds like' (homophone) clue.
'cologne' becomes 'scent' (cologne is a type of scent).
'is popular' becomes 'in' ('in' can mean trendy).
'with' is a charade indicator (letters next to each other).
'the foreign' becomes 'el' ('the' in Spanish).
'scent' sounds like 'sent'.
'sent'+'in'+'el'='SENTINEL'
(Other definitions for sentinel that I've seen before include "One watches" , "One on guard" , "Watchman" , "Guard - ten lines (anag)" , "Soldier keeping watch" .)