Validation rule

Hi,

I created a validation rule on a custom object to "lock" records (prevent any changes) whenever checkbox final__c is checked. 

The condition in the validation rule is 

final__c = true

Problem is that once I enable the validation rule, it throws the Error as I am checking final__c and trying to save. I want it to throw the error only after the final__c has been checked and saved.

Any thoughts on how to resolve this?