I'm not even sure it is necessary to audit the Defense Dept., seeing as how
A) DOD already has its own in-house finance and auditing staff
B) a big chunk of the defense budget is classified, and if Rand Paul thinks the President and/or Secretary of Defense will authorize the sharing of that information with an outside auditor he is kidding himself
C) the President is commander-in-chief, and as such, already knows all the fucked-up shit our military and intelligence communities are doing
D) demanding an audit of everything is really about creating the appearance of accountability and transparency rather than actually making anyone/anything accountable and transparent