I've difficulties surviving in the last campaign mission in Warcraft 3 on the highest difficulty settings. After capturing the mines and building as much of an army as possible, I get decimated by the incoming forces faster than I can rebuild. I usually end up as sole survivor (Hu/Orc base destroyed) after 10 minutes. I tried various stuff, including building wells near the place of battle and walls of ancient protectors, but to no avail.

I'm wondering if it is actually that hard, or if I just do something wrong. I was about level 30 on the solo ladder so I think my micro and macro is not utterly crappy in general.