Keep at it, being more than strict (9)
I believe the answer is:
persevere
'keep at it' is the definition.
(I've seen this before)
'more than strict' is the wordplay.
'more than' becomes 'per' (I can't justify this - if you can you should give a lot more credence to this answer).
'strict' becomes 'severe' (I've seen this in another clue).
'per'+'severe'='PERSEVERE'
'being' acts as a link.
Can you help me to learn more?
(Other definitions for persevere that I've seen before include "Go on in spite of setbacks" , "Continue despite difficulties" , "Battle on" , "Be unwilling to stop" , "Serve peer (anag.)" .)