Ask HN: Protecting your Sites/Services from Unwanted Traffic?

So... If PoW (proof-of-work) schemes like Anubis ultimately don't' work in practise, because Bots/Crawlers are increasingly using headless browsers, are able to solve captures, proofs, etc;

What options do we have realistically to filter out or block unwanted traffic?

What clever schemes can we come up that don't rely on centralised serices like Cloudflare?