Protected area student found in dojo (5,4)

I believe the answer is:

green belt

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'protected area' is the definition.
(green area which cannot be built on)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for green belt that I've seen before include "protected lung" , "Zone where development is banned (in theory)" , "Circle determined to preserve" , "area of open land near town" , "Undeveloped land surrounding a city" .)

I've seen this clue in The Independent.

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