2. Create fake html elements and put unique strings inside. And you can search that string in search engines for finding similar fake sites on different domains.
3. Create fake html element and put all request details in encrypted format. Visit adversary's website and look for that element and flag that ip OR flag the headers.
4. Buy proxy databases, and when any user requests your webpage, check if its a proxy.
5. Instead of banning them, return fake content (fake titles and fake images etc) if proxy is detected OR the ip is flagged.
6. Don't ban the flagged ip's. She/He's gonna find another one. Make them angry and their user's angry so they give up on you.
7. Maybe write some bad words to the user on random places in the HTML when you detect flagged ip's :D So the user's will leave the site and this will reduce the SEO point of the adversary. Will be downranked.
8. Enable image hotlinking protection. Increase the cost of proxying for them.
9. Use @document CSS to hide the stuff when the URL is different.
10. Send abuse mail request to the hosting site.
11. Send abuse mail request to the domain provider.
12. Look for the flagged IPs and try to find the proxy provider. If you find, send mail to them too.
Edit: More ideas sparkled in my mind when I was in toilet:
1. Create fake big css files (10MB etc). And repeatedly download that from the adversary's website. This should cost them too much money on proxies.
2. When you detect proxy, return too big fake HTML files (10GB) etc. That could crash their server if they load the HTML into the memory when parsing.