I don't think simply the complexity of structures can prevent collusion between people with similar class and school backgrounds. This is one of the things in life that is simple: watchdogs, sheepdogs, need a personal incentive for catching wrongdoers, and the closer they are to each other culturally, the higher is the danger of old boys networds, the stronger this needs to be. I think complex structures are just a make-believe thing, ultimately it is still about whether I will incriminate some old buddy who I go regularly drinking with who works in a department of my organization a watchdog is or not. It is one of the things that is hard to do but the underlying logic is simple.

For example, Byzantine emperors made sure their bodyguards come from feuding Norse tribes, to prevent collusion (as a conspiracy to kil him). This is one of the simple ways of doing so. If it was on me, I would try putting people from lower-class backgrounds who are very, very suspicious and disliking of silver spoon folks into watchdog positions.