But people that have experience building decentralized protocols will tell you that it's a very hard problem to solve, for many reasons.
This is an engineering community, so I believe that it's important to focus on things that exist today. Not on speculative solutions.
This post (also, coincidentally by Vitalik) talks about different levels of collusion (from unsophisticated to sophisticated) https://vitalik.ca/general/2019/04/03/collusion.html
Gitcoin's approach thus far has been to stop collusion from unsophisticated actors, then progressively get more organized (as more money gets involved, and as we learn from each round) about stopping collusion from more sophisticated actors.
This thread talks about some collusion that we founnd in Round 5. https://twitter.com/owocki/status/1250097472694702080