Completely block comments with too many links

I guess this question must have been asked by other people before, but I have not been able to find a solution yet. I think a comment with more than 10 or even 30 links is apparently a spam and I want to completely block such comments instead of just marking them as spam and letting them live in my database for a month (default setting by Akismet). The reason for doing so is Akismet sometimes has false positives (classified as spam but not spam) and these comments are difficult to be found out in the flood of spam comments.

I wonder if there is a way to stop such spams forever. The only way in WP is to hold comments with a certain number of links in the queue.

Thanks!