I'm looking to override the unlink method for account_invoice and I need it to check who the user is (namely if the user is super admin). For this I need to add parameters cr, and uid to it. Obviously raises an exception as the function calling the unlink method only supplies one arguement. I'm looking for the web controller so that I can modify add the additional arguements there. 

First - does this makes sense as a way to attack the problem?

Second - in which directory can I find the relevant web controller?