Secret of reform is without obligation (4,4)
I believe the answer is:
scot free
'without obligation' is the definition.
I can't judge whether this defines the answer.
'secret of reform' is the wordplay.
'reform' indicates an anagram (letters in a new form).
'secret'+'of'='secretof'
'secretof' with letters rearranged gives 'SCOT-FREE'.
'is' acts as a link.
Can you help me to learn more?
(Other definitions for scot free that I've seen before include "Not getting penalty - say" , "undamaged" , "It may be got off" , "Unpunished" , "(Get away) incurring no penalty" .)