The mod rewrite you suggested offer some protection. When I had similar problem a few years ago, here are other things I did in addition to the mod_rewrite:
1. Get strong links to your site so that your site is at least stronger than the copycat.
2. Rewrite some of the contents of your site so that its not a duplicate any more but a different version of the one that was copied.
3. Update you site regularly so that the copycat cannot keep up.
4. use a more aggressive exclusion robots.txt file, allowing ONLY the big 3 crawlers.
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