Wash and dry all fruit before cutting.
Slice both ends off the first watermelon.
Stand it upright and trim off the rind.
Cut one 3-inch round for the bottom tier.
Repeat with the second watermelon for a smaller top tier.
Pat the watermelon rounds dry with paper towels.
Place the larger round on a cake stand or platter.
Center the smaller round on top.
Add short skewers through the center if the layers need support.
Decorate with berries, kiwi, grapes, pineapple, melon balls, and mint.
Use toothpicks to secure fruit on the sides.
Brush fruit lightly with lime juice or honey, if using.
Chill the finished cake for 30 minutes before serving.