Arrange watermelon in a single layer in two 9-by-13-inch baking dishes. Bring sugar, water, tequila, and Triple Sec to a boil in a small saucepan. Cook, stirring, until sugar dissolves, about 1 minute. Let cool slightly. Pour syrup over watermelon wedges, and refrigerate for at least 45 minutes.
Remove watermelon from syrup, and arrange on a platter. Squeeze limes over melon, and season with salt.