A good conflict of interest policy should seek to eliminate not only actual conflicts but also the appearance thereof.
This is what the US Congress is trying to do by banning members from trading individual stocks. It is not enough to review a trade after it has been made because, in many cases, the trade was made after a member received information from a classified briefing.
Take a look at your conflict policies, gift policies, even your anti-corruption policies. Are they filled with detailed prescriptions about who-can-receive-what-from-whom-and-under-what-amount? If so, it could be a sign that the activities you are trying to regulate might simply need to be prohibited.