If you really wanna filter the bulls**t, the best thing you can do is block ENTIRE chinese and australian IP space. You can find the latest IP blocks for any given country here:
http://www.apnic.net/apnic-bin/ipv4-....pl?country=cn
http://www.apnic.net/apnic-bin/ipv4-....pl?country=au
Simply add these blocks to your IPtables rules and I GUARANTEE this will eliminate 99.9999% of the spam and foreign attacks. I do this as a rule. I have NO REASON to do business with anyone in China or Australia.
A more interactive way to achieve this is to install the GeoIP module for Apache. It looksup every hostname/IP in the GeoIP table and determines the country. You can then set rules based on visitor country.