Underground guards in Zurich? (6)

I believe the answer is:

gnomes

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'guards in zurich?' is the definition.
The answer and definition can be both people as well as being plural nouns.
Maybe there's a link between them I don't understand?

I don't understand the remainder of the clue.

Can you help me to learn more?

(Other definitions for gnomes that I've seen before include "Legendary little figures, in the garden perhaps" , "Snog me (anag)" , "Legendary dwarfs" , "Influential dwarfs from Zurich?" , "Ornamental garden figures" .)

I've seen this clue in the Evening Standard.

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