Guardian's right for a time for deputy head (9)

I believe the answer is:

prorector

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'guardian's right for a time' is the definition.
I don't know anything about this answer so I cannot judge whether it can be defined by this definition.

'for deputy head' is the wordplay.
'for' becomes 'pro' (as in being 'pro' something).
'deputy head' becomes 'rector' (I can't explain this - if you can you should believe this answer much more).
'pro'+'rector'='PRORECTOR'

Can you help me to learn more?

I've seen this clue in The Guardian.

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