Appear behind guard (4,5)
I believe the answer is:
look after
'guard' is the definition.
(thesaurus)
'appear behind' is the wordplay.
'appear' becomes 'look' (synonyms).
'behind' becomes 'after' (eg after or behind someone in a queue).
'look'+'after'='LOOK AFTER'
(Other definitions for look after that I've seen before include "Take care of" , "Supervise" , "Peer trying to find" , "nurse" , "Tend" .)