In sum: "In Mr. Ipeirotis’ view, if there’s one big lesson from his semester in the cheating trenches, it’s this: Rather than police plagiarism, professors should design assignments that cannot be plagiarized.
How? He suggested several options. You could require that projects be made public, which would risk embarrassment for someone who wanted to copy from a past semester. You could assign homework where students give class presentations and then are graded by their peers, ratcheting up the social pressure to perform well. And you could create an incentive to do good work by turning homework into a competition, like asking students to build Web sites and rewarding those that get the most clicks."