I would say that the root cause lies in our human nature, that we move towards organising into groups. Logically, not all these groups can be altruistic in outlook, thus there needs to be oversight from a "stronger grouping". So, power gathers, and the best we can do is to make sure the power centres are sufficiently dispersed and balanced, and fettered with accountable restraints (like elections).
Partnerships and co-ops, would that work on a large scale, and what prevents them falling to corruption (like other long term power centres)? I would be skeptical to the idea that they are immune, but perhaps they have structures that might be adopted to evolve a democracy?
At the moment, the answer to "who guards the guardians?" is: nobody.
Everything has been bought.
I myself concentrate on the sciences; it's all been bought and being weaponised. Something as simple as peer-review is laughable for any product-based research, and there is probably more science to be found at the patent office than in public literature.
I could go on, but the "protection systems" have all failed or are failing.
People sense it, but few are able to articulate it. In the latest IPSOS Global Survey, there is a widespread malaise around the world but most people are waiting for a miracle or messiah, a trusted leader, to guide them. That doesn't strike me as the soil upon which we will see any revolution, material or spiritual, just a slave's desire for some peace.
This I think is the greatest reason for evolving our democratic systems. I don't think getting rid of guardians is the solution, but we do need to stop appealing to systems and paper documents that have far outlived their usefulness. The basic concept is good, but the application is flawed or at least no longer keeping up.
On the Science side of things, marketing has definitely taken over, especially in product based research. I'm not sure how strong the consumer protection is for your country, but this is supposed to be part of the defense, in addition to a scientifically literate population (ha ha... Wishful thinking! ).
I'm not sure all the protections are failed or failing, but they sure could use a bit of shoring up. At the moment, the penalties for corporate wrong doing are a joke.
I really think the place to start is by fixing up the systems that we use to elect our representatives who then decide upon laws and policies. Sortition, for me, if well implemented could go a long way to combating corruption in Western countries.