You cannot create a good enough ethical mousetrap - humans are vastly creative (even at fraud). The mishaps at LIBOR, VW, 2008 financial crisis, Deepwater Horizon, Wells Fargo all happened at businesses which had multiple layers of controls.
So what can you do? Create an ethical culture - it sounds a glib thing to say (for a consultant), but if we want ethical organizations, free from fraud and from social and environmental harms, that is what is required.
One way to do that is to create "ethics stories" - which uses stories as units of cultural transmission. In this short clip, I offer examples from BP and Shell - and note that fact that Microsoft is trying to do this with innovation.