On still water, I can skip a rock upwards of a dozen times, ending in a kind of ski-slide until it stops and sinks. The trick is to get a rock of sufficient heft and flatness to really make it work. But it's not all that difficult.
Another fun trick is to see how far you can skip that first bounce. You need to hit the water at a slightly steeper angle for that.
Then again, I was a baseball pitcher in younger days, and can still throw pretty hard. Maybe it helps if you, like me, are a lefty (coriolis effect, ya know).
caw