Life in the grey area: Private WOW server under repeat DDOS attack.

Arena tournament staff: "As most of you might have noticed, we are currently under a huge Ddos attack and are doing our best to resolve the issue. The attacker is the same guy who threatened us a while ago (Trentddos) but the attacks have increased by size. We are not able to tell yet for how long we will stay offline but we're doing everything in our power to get the server running. We're thankful for everyones support and patience."

What sort of measures could you take to prevent this sort of thing?