If you have to HAMMER at a stake to drive it, you're better off moving the tent stake to one side - or moving the whole tent - or tying off to a rock - or some other way of getting the same result. Hammering it in rocky soil will bend it 99 times out of 100.

I generally find a flatish, smooth rock and use it to protect the butt of my hand as I PRESS the stake into recalcitrant ground. Once it is well-started, I may step it the rest of the way in with my foot.