Two posts in a row, the holiday plans for this year

Last year was cycling from Oudenaarde to Santiago de Compostella on a tandem. Anyone who wanted could follow that on Twitter. This year the plan is rafting on the Grand Canyon or somewhere in the neighborhood. That will be a bit more organised, going down a white water river safely can't be done without preparation. Advice/tips on what are great stetches to do are welcome. We are not experienced rafters, but not interested in you family trip type rafting experience either. We are at ease in normal water, we did some rafting ad hydrospeed many years ago.