Heads off to deal with this gatekeeper? (8)

I believe the answer is:

cerberus

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'gatekeeper?' is the definition.
(three-headed guard dog in Greek mythology)

I can't explain the rest of the clue.

(Other definitions for cerberus that I've seen before include "Guardian dog of Hades" , "Three headed guard dog of Hades" , "Mythical three-headed watchdog guarding Hades" , "underworld guard" , "Three-headed guard dog" .)

I've seen this clue in The Independent.

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