1. In a blender or food processor, place watermelon, 2 tablespoons fresh lime juice and 2 tablespoons agave nectar. Cover and blend or process until smooth. Strain mixture through a fine-mesh sieve set over a medium bowl; discard pulp.
2. Pour watermelon mixture into 10 (3-ounce) pop molds. Cover with lid.* Insert craft sticks. Freeze for 4 hours or until firm.
3. In a blender or food processor, combine cucumber, remaining 1 tablespoon lime juice and remaining 2 tablespoons agave nectar. Cover and blend or process until smooth. Stir in mint. Remove lid from pop molds. Pour cucumber mixture on top of frozen watermelon mixture. Cover with lid and freeze for 4 hours or until firm.
4. To unmold paletas, dip molds into cool water until paletas loosen from molds. Gently remove frozen paletas from molds and transfer to a baking sheet lined with parchment paper. Freeze at least 10 minutes or lightly cover with plastic wrap and store in freezer until ready to serve.

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*If pop molds have individual lids with attached sticks, cover molds with foil. Cut small slits in foil and insert craft sticks into each pop.