"Year of the Watermelon" Sparks Harvest Trepidation

The National Garden Bureau has declared 2013 the Year of the Watermelon. Yes, everyone loves watermelon, especially my kiddo, but growing them? Or, to be more clear on that question, growing them and harvesting them at the right time? Well, I have successfully grown watermelons in my garden. The melon above was part of the 2011 crop that encircled the bed of strawberries. I had one plant that produced 4 melons that year. I fretted about when to know if they were ready to harvest. I researched online. I spoke with neighbors and other gardeners. I tapped. I checked the bottom for a little yellowing. I checked the skin "toughness." I checked the stem for a bit of withering. And I harvested every single one of those melons at the "wrong time." Three were not entirely ripe, and the fourth was overripe. So a declaration of "Year of the Watermelon" means a new challenge. What tips do you have for ensuring a perfect pick?