Insert a toothpick into each cube of watermelon, freeze on a plate or chopping board lined with baking paper for approx. 1 hr.
Melt the chocolate icing in a bain-marie, pour into separate bowls. Dip the watermelon cubes ¾ of the way into one or other of the bowls of icing. Keep melting the chocolate so that it remains runny. Leave the melon cubes to dry on a sheet of baking paper.