My two can play pretty rough too. Casie is 1 lb lighter than Scottie but she is 10 times as feisty! Casie is a big leg biter. Scottie is a growler and humper. I don't know why, but sometimes he loses sense of direction and humps her face. Then, Casie can be pretty mean and go for his privates!
They absolutely love chasing and wrestling each other though!
When they play too rough and one of them yelps, I usually quickly ask them "what happened?!". They'll look guiltily at me with the "uh oh, busted..." face and then stop playing.