Decorator’s accessory: staff retaining piece to copy (7,4)

I believe the answer is:

masking tape

'decorator's accessory' is the definition.

'staff retaining piece to copy' is the wordplay.
'staff' becomes 'mast'.
'retaining' indicates putting letters inside.
'piece' becomes 'king' (king is a kind of piece**).
'to copy' becomes 'ape' ('ape' can be a synonym of 'copy').
'mast' going around 'king' is 'maskingt'.
'maskingt'+'ape'='MASKING TAPE'

(Another definition for masking tape that I've seen is " I keep coat off".)

I've seen this clue in The Times.

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