Engineer tightens guard that's not being used (9,4)

I believe the answer is:

gathering dust

'not being used' is the definition.

'engineer tightens guard' is the wordplay.
'engineer' indicates anagramming the letters.
'tightens'+'guard'='tightensguard'
'tightensguard' with letters rearranged gives 'GATHERING DUST'.

'that's' is the link.

I've seen this clue in The Guardian.

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