There's not a lot you can to do prevent your site from being targeted by a DDoS attack.
If you are unfortunate enough to get DDoS'd you probably have enough money to pay for a service like Prolexic, etc that will shield you almost entirely from DDoS attacks. DDoS protection services are used to people signing up during an attack, so they are usually pretty quick to implement. The downside is that services like this tend to be expensive and can mess up regular traffic (especially if you are providing an API).
If you are unfortunate enough to get DDoS'd you probably have enough money to pay for a service like Prolexic, etc that will shield you almost entirely from DDoS attacks. DDoS protection services are used to people signing up during an attack, so they are usually pretty quick to implement. The downside is that services like this tend to be expensive and can mess up regular traffic (especially if you are providing an API).