Experienced engineer bored tunnels around Spain (5,4,4)

I believe the answer is:

under ones belt

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'experienced' is the definition.
I know nothing about this answer so I can't judge whether it can be defined by this definition.

'engineer bored tunnels around spain' is the wordplay.
'engineer' indicates anagramming the letters.
'around' is an insertion indicator.
'spain' becomes 'e' (abbreviation for Espana).
'bored'+'tunnels'='boredtunnels'
'boredtunnels' with letters rearranged gives 'underonesblt'.
'underonesblt' enclosing 'e' is 'UNDER ONES BELT'.

Can you help me to learn more?

(Other definitions for under ones belt that I've seen before include "Successfully achieved" , "Safely achieved" , "Digested; (experience) assimilated" .)

I've seen this clue in The Independent.

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