Head off before escape (7)

I believe the answer is:

prevent

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'head off' is the definition.
'prevent' can be an answer for 'head' (thesaurus). I'm not certain of the 'off' bit.

'before escape' is the wordplay.
'before' becomes 'pre' (prefix meaning 'before').
'escape' becomes 'vent' (I've seen this in other clues).
'pre'+'vent'='PREVENT'

Can you help me to learn more?

(Other definitions for prevent that I've seen before include "Stop from happening" , "Keep from arising" , "Thwart" , "Stop, avert" , "Stop (an action)" .)

I've seen this clue in the Sydney Morning Herald.

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