Level deck shelf long off-limits (7)

I believe the answer is:

echelon

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

I can't explain the remainder of the clue.

(Other definitions for echelon that I've seen before include "Level or rank of authority, upper or lower" , "Body of troops arranged in a line" , "Leech on (anag.)" , "Level of people in organisation" , "Ladder formation" .)

I've seen this clue in the Sydney Morning Herald.

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