Ollie’s partner almost finished composing rude song “stay firm” (5,4,6)
I believe the answer is:
stand ones ground
'stay firm' is the definition.
I don't know anything about this answer so I can't tell whether this works.
'ollie's partner almost finished composing rude song' is the wordplay.
'ollie's partner' becomes 'stan' (as in Stan Laurel and Oliver Hardy).
'almost finished' becomes 'don' (I can't explain this - if you can you should give a lot more credence to this answer).
'composing' indicates an anagram.
'rude'+'song'='rudesong'
'rudesong' is an anagram of 'esground'.
'stan'+'don'+'esground'='STAND ONES GROUND'
Can you help me to learn more?
(Other definitions for stand ones ground that I've seen before include "Refuse to move" , "Maintain personal position" .)