Refusal to head leading prison - it sounds difficult (2,6)

I believe the answer is:

no picnic

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

'difficult' is the definition.
(thesaurus)

'refusal to head leading prison it sounds' is the wordplay.
I cannot quite understand how this works, but
'refusal' could be 'no' and 'no' is found within the answer.
The remaining letters 'picnic' is a valid word which might be clued in a way I don't see.
This explanation may well be incorrect...

Can you help me to learn more?

I've seen this clue in The Irish Times.

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