How do you discourage a dog from biting while playing?

She's clearly having fun, running around in circles, chewing sticks, and finding and eating cat poop. And I don't want to discourage her from having fun when I take her outside (except for the cat poop thing -- that needs to stop).

But she seems to have the idea that jumping up and biting my wrists or my ankles is a fun game that we both enjoy, and she seems to be getting more agressive about it.