When you are ready to make the cocktails, place drinking glasses in the freezer to chill. Place your watermelon, ice, tequila, orange liqueur, lime juice and agave into a high-speed blender
. Blend until smooth. If your blender is stuck, you can move everything around a bit with a tamper or spoon (while turned off). You can also add a few splashes of water to help keep things moving. You can even use a few pieces of fresh watermelon.