@christian: If the visits are actually reaching your site (unlike the ones in the link I posted above), then you can use Advanced Blocking, as long as there is something consistent in the referers. For example, if you have host1.badsite.com and host2.badsite.com, you can block “*.badsite.com”.
More details on advanced blocking are available here:
How to block a referer
If you need more information, can you make a separate post from the main forum page? (here) The www.remarpro.com forum rules ask us to keep each person’s questions separate, and that also makes it easier to be sure we can read each new post. Thanks!
-Matt R