…& oblige erosion? Hardly a problem (2,3,4)

I believe the answer is:

no big deal

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'oblige erosion?' is the definition.
I can't tell whether this definition defines the answer.

'hardly a problem' is the wordplay.
'hardly' becomes 'no' (eg 'hardly a meal' means 'not a meal' or 'no meal').
'a problem' becomes 'bigdeal' (I can't justify this - if you can you should believe this answer much more).
'no'+'bigdeal'='NO BIG DEAL'

Can you help me to learn more?

I've seen this clue in the Sydney Morning Herald.

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