One time I buckled a board I held on and very lucky I did because break was a shallow coral reef that tubed top to bottom. Ever since duck diving regardless of bottom I hold on death grip rails and try to get as deep as possible. Seems to help my leashes last longer as wellDuck diving is not something I think consciously about, the only thing would be to try and go deeper depending on the amount of whitewater and power in the waves. I don't try and hang on if it will be unsuccessful, just let the board go underwater and hopefully it's still attached to the legrope when you resurface.