Contributor Willard Dix writes: Many years ago I worked briefly for a marketing agency whose clients included colleges and universities. The Internet was burgeoning, and colleges were developing their websites. One of our jobs was to steer potential students to those sites. But we also wanted to know how they got to them: Through the postcard we sent them? The email we used if we had it? An ad in a publication? To that end, we developed a unique web address for each medium that would tell us which method was most effective. That enabled institutions to shift their budgets appropriately and attempt to avoid John Wanamaker's problem: "Half the money I spend on advertising is wasted; the trouble is I don't know which half."