I could certainly try floating on my back... but I already got ocean-water in my ears from swimming normally, so maybe that's a bad idea.

[Just thinking about it makes him need to shake his head sharply, just like a cat getting something out of his ear.]

When my mentor was training me to fight, the main thing she taught me was that if I was trapped, I should go limp until my opponent hesitates, and then I can strike. I tried something similar while I was helping folk out of the ocean - going limp when the waves hit me, and holding my breath, and it worked pretty well.