Source of protection, albeit with strings (5)

I believe the answer is:

apron

I'm a little stuck... Click here to teach me more about this clue!

'source of protection' is the definition.
'apron' can be an answer for 'protection' (protective garment). I am unsure of the 'source of' bit.

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for apron that I've seen before include "Kitchen garment or aerodrome strip" , "Pinny -part of the fairway leading onto the green" , "Garment for protection" , "edge" , "Extension of stage in front of curtain" .)

I've seen this clue in the Evening Standard.

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