If you are, there's little future for you as a guard (4,7)

I believe the answer is:

poor lookout

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'if you are there's little future for' is the definition.
I don't know anything about this answer so I can't judge whether this works.

'as a guard' is the wordplay.
'as' becomes 'poor' (I am not sure about this - if you are sure you should believe this answer much more).
'a guard' becomes 'lookout' (lookout is a kind of guard).
'poor'+'lookout'='POOR LOOKOUT'

'you' is the link.

Can you help me to learn more?

I've seen this clue in the Evening Standard.

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