Sound advice for securing a small case (6)

I believe the answer is:

locket

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'case' is the definition.
(I know that locket is a type of case)

I don't understand the remainder of the clue.

(Other definitions for locket that I've seen before include "Small case on pendant, may hold photo" , "Small pendant containing photo" , "Lucy" , "Small ornamental case for photo etc." , "Ornamental case on necklace for memento" .)

I've seen this clue in The Globe and Mail.

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