Relaxed about extra secure borders (2,4)

I believe the answer is:

at ease

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'relaxed' is the definition.
(similar in meaning)

'about extra secure borders' is the wordplay.
'about' becomes 'a' (abbreviation in Chambers).
'extra secure borders' becomes 'tease' (I can't explain this - if you can you should give a lot more credence to this answer).
'a'+'tease'='AT EASE'

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(Other definitions for at ease that I've seen before include "Relax - that's an army order" , "Relaxed, not tense - that's an order" , "In a relaxed attitude" , "unworried" , "Free from anxiety" .)

I've seen this clue in The Independent.

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