Cantelopes smell sweet and the vine end just falls off. Watermelon your supposed to knock on it and it sounds hollow. Nothing worse than cutting open an unripe watermelon after all that anticipation. Thing is unless you have a lot I don't think the sound is going to mean anything to the inexperienced. I have 2 and they both do sound different, but which is ripe?
I put all my melons up on inverted plant pots today. Otherwise the melon can rot from the ground, but even more frustrating is when a animal tunnels inside from the bottom and has a feast leaving a perfect LOOKING melon behind. It also lift them into the sun and is supposed to make them sweeter.