This is something that I recently posted about (creating a downvote bot to target these self-vote rings). It's on the backburner for the time being, but it's something I will eventually get going.

It's also important to keep some perspective, I think. The sums involved (i.e. proportions of the total reward pool) are tiny, as far as I can tell. It's why I shuffled my anti-vote-farming bot project down my to-do list.