aristotle - 11:47 am on Oct 10, 2011 (gmt 0)
Is it not best to do a 301 permanent rewrite so that you benefit from them? Particularly if you point the rewrite to the actual page that the referring site is trying to take its users to on your site.
If this trend continues, you could end up trying to do hundreds, or even thousands, of individual re-directs. Might not be worth the time and trouble. Instead, I just have an error page with a link to the home page.