You could try to block the URL in robots.txt like Sanket says below, but at the end of the day, the link's still pointing to your website and therefore Google will still see it. If I'm not mistaken, Bing has launched their disavow tool already (Ref: http://www.serperture.com/blog/link-building/disavow-link-tool-block-bad-incoming-links), so perhaps you should at least start there?

David, SaraSEO states, "I cannot get these websites to remove our links" above, so I would say that she has tried that to no avail, unfortunately.

Hi SaraSEO,

If I've understood correctly, you have backlinks to your website that you would like to have removed as they're harming your domain's authority. If that's the case, then the best thing you can do is Google about Google's disavow tool and list the domains as unwanted.

Unfortunately negative SEO is a topic that's been discussed in great detail and there are many opinions, but listing these bad domains as unwanted is a wise move. Blocking the IP addresses on your production firewall, isn't going to stop Google from seeing the association unfortunately.

Hope that helps!