[rdb3]

Can we not use these lists or some internal property of said server to deny access by anonymous and high-anonymous proxy servers?

That would be a piece of cake, especially if this site uses Apache.

[Lazamataz]

[Using lists or some internal property of said server to deny access by anonymous and high-anonymous proxy servers] would be a piece of cake, especially if this site uses Apache.

Then let us make it so.