Slice a small portion of the bottom of the watermelon and then stand it on a cutting board. Cut rind (both green and white) off entire watermelon. Slice watermelon into 3 (or more) discs about 2-inches thick. Trim each disc into rounds, gradually making each disc smaller than the last to create tiers. (TIP: Use 3 different size plates or cake pans to create perfect circles by placing the plate or pan on each slice and cut around the edges. I used a 9-inch, 6 inch and 4 inch pan as a guide.) Place several layers of paper towels on a baking sheet and lay each round on the paper towel. Cover with more paper towels and refrigerate for several hours or overnight. (The liquid from the watermelon will drain into the towels, drying it out, which insures that the icing will adhere to the watermelon.) When ready to serve, mix together Cool Whip, sour cream or yogurt and two heaping tablespoons of instant pudding until mixture thickens, about 2 minutes. Place icing mixture in a piping bag. Place the large bottom round of the watermelon cake on a platter. Build your layers by spreading a small amount of icing in between each layer and pressing down. Pipe icing around the tiers of the cake and press fruit into the icing. Garnish around the bottom layer with fruit. Keep refrigerated until ready to serve.