Veteran alerts God when tottery (3,6)

I believe the answer is:

old stager

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'veteran' is the definition.
(I know that veteran can be written as old stager)

'alerts god when tottery' is the wordplay.
'alerts god' anagrams to 'OLD STAGER'.
However, I'm unsure how the anagram is indicated.

Can you help me to learn more?

(Other definitions for old stager that I've seen before include "One who's experienced a lot" , "veteran" , "senior citizen" , "expert" .)

I've seen this clue in The Telegraph.

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