Theirs is a boring occupation (8)

I believe the answer is:

drillers

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

'theirs' is the definition.
I don't know anything about this answer so I cannot tell whether this works.

'boring occupation' is the wordplay.
'boring' becomes 'drill' (I've seen this before).
'occupation' becomes 'ers' (I am not sure about this - if you are sure you should give a lot more credence to this answer).
'drill'+'ers'='DRILLERS'

'is a' acts as a link.

Can you help me to learn more?

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

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