### Clue: Proof of saint's transfiguration in balance (9)
### Answer: RESISTANT 
 ### Explanation: Definition: Proof
 **Anagram of**(…'s transfiguration) SAINT **contained in**(in) REST(the balance;that which is left over).
Defn: Being able to withstand;being impenetrable, impervious or invulnerable, as is "foolproof".