Limit all non-USA crawlers? The USA traffic is probably the worst offenders for scraping content.
Personally, I wouldn't even bother with this. As long as other sites aren't outranking you with your own content then I don't see a problem. If they are outranking you with your own content, then you need to evaluate your SEO strategy.
You could add some unique words/sentences to the pages which will make googling for "mirrors" easy (i.e. automated) so sending copyright notices to Google can be almost fully automated.
Personally, I wouldn't even bother with this. As long as other sites aren't outranking you with your own content then I don't see a problem. If they are outranking you with your own content, then you need to evaluate your SEO strategy.