Crossword Genius

What made the chicken opt for a secure crossing (10)

Ross

I believe the answer is:

checkpoint

I'm a little stuck... Click here to teach me more about this clue!

'a secure crossing' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'what made the chicken opt' is the wordplay.
'chicken opt' can be anagrammed to 'CHECKPOINT'.
But, I'm not sure how the anagram is indicated.

'for' acts as a link.

Can you help me to learn more?

(Other definitions for checkpoint that I've seen before include "border post" , "where travellers are inspected" , "Charlie, perhaps" , "place at frontier?" , "Where on inspection one may cross" .)

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