Posted home, the Spanish guard (8)
I believe the answer is:
sentinel
'guard' is the definition.
(sentinel is a kind of guard)
'posted home the spanish' is the wordplay.
'posted' becomes 'sent' ('send' can be a synonym of 'post').
'home' becomes 'in' ('he's home' can mean 'he's in').
'the spanish' becomes 'el'.
'sent'+'in'+'el'='SENTINEL'
(Other definitions for sentinel that I've seen before include "One watching" , "Guard who stands and keeps watch" , "One watches" , "Watching guard" , "One stands and keeps watch" .)