Grasping tail in dark, beware rat that's mistaken for mole

I believe the answer is:

breakwater

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'for mole' is the definition.
('breakwater' can be a synonym of 'mole')

I can't explain the remainder of the clue.

(Other definitions for breakwater that I've seen before include "mole" , "Groyne" .)

I've seen this clue in The Telegraph.

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