Are going to stay put, in the main (4,6)

I believe the answer is:

drop anchor

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'stay put in the main' is the definition.
'drop anchor' can be an answer for 'stay' (thesaurus). I'm not certain of the 'put in the main' bit.

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for drop anchor that I've seen before include "Moor away from land" , "Secure a vessel offshore" .)

I've seen this clue in the Evening Standard.

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