Keep your knees bent and together. Cross your ankles. Use only your arms to scull water. You want to create a "modesty pocket" of murky water beneath you. If the pool is crystal clear, switch to a tight eggbeater kick (like water polo players use). It creates turbulence that refracts light.
There are few phrases that can clear a swimming pool faster, or induce a more visceral sense of sympathetic panic, than the frantic shout: "My swimming trunks have been sucked off!" It is a scenario that sounds like the setup of a slapstick comedy, but for those who experience it, it is a moment of genuine terror, embarrassment, and potential danger.