Guarding hard border (7)

I believe the answer is:

hedging

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'guarding' is the definition.
Although both the answer and definition are present participle verbs, I can't see how one could define the other.

'hard border' is the wordplay.
'hard' becomes 'h' (abbreviation used in pencil classifications).
'border' becomes 'edging' (edging is a kind of border).
'h'+'edging'='HEDGING'

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I've seen this clue in The Telegraph.

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