I have been speculating on adding a tar pit on my personal web site. A script that produces a page of random nonsense and random looking links to the same script. The thing not linked to anywhere, but explicitly forbidden on robots.txt. If the crawlers start on it let them get lost. Bit of rate limiting should keep my server safe, and slow down the crawlers. Maybe I should add some confusing prompts on the page as well... Probably I never get around to it, but the idea sounds tempting.