Cannabis finally concealed for border (3)

I believe the answer is:

hem

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

'for border' is the definition.
(I've seen this before)

I don't understand the remainder of the clue.

(Other definitions for hem that I've seen before include "Double-backed cloth border" , "Express hesitation" , "may attract attention" , "Stitched edge of garment" , "Part of skirt" .)

I've seen this clue in The Times.

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