Alarming trouble on the border (8)

I believe the answer is:

marginal

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'on the border' is the definition.
I can't tell whether this definition defines the answer.

'alarming trouble' is the wordplay.
'trouble' indicates anagramming the letters.
'alarming' with letters rearranged gives 'MARGINAL'.

Can you help me to learn more?

(Other definitions for marginal that I've seen before include "Alarming (anag) - too small to matter" , "On the edges of" , "Borderline" , "On the fringes" , "on border" .)

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

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