Reliable lad looks after ponies (6,3)

I believe the answer is:

stable boy

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

'reliable lad' is the wordplay.
'reliable' becomes 'stable' (I can't justify this - if you can you should believe this answer much more).
'lad' becomes 'boy' (I've seen this in another clue).
'stable'+'boy'='STABLE-BOY'

Can you help me to learn more?

I've seen this clue in The Mirror.

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