Stop being careful and dismiss personal security (4,4,5)

I believe the answer is:

drop ones guard

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'stop being careful' is the definition.
I know nothing about this answer so I can't tell whether this works.

'dismiss personal security' is the wordplay.
'dismiss' becomes 'drop' (synonyms).
'personal' becomes 'one's' (belonging to oneself).
'security' becomes 'guard' (I've seen this in another clue).
'drop'+'ones'+'guard'='DROP ONES GUARD'

'and' is the link.

Can you help me to learn more?

(Other definitions for drop ones guard that I've seen before include "drive train off alone?" , "Take a risk" .)

I've seen this clue in The Daily Express.

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