Ah, 8 month old males--if they're not acting like clueless dorks they're acting like cocky punks. Honestly though, your description of his "attacks" isn't really very descriptive. I don't mean it to be insulting, it's just that more description of the interaction is needed for anyone to offer you meaningful advice. What specifically does each dog do during the interaction? What do his ears look like--pinned back, relaxed, alert and forward? What is his mouth doing--tight lipped, tongue out, lips raised? How does he pin her--box her with paws, bite at her neck, body slam, goes for her legs? Is he pinning her, or is she just flopping over to get him to stop? Does he bite her? Is there any punctures or just a lot of swapping of spit? How long do the altercations last? What are they doing right before it happens and how do they behave toward each other right after? Look closely for signals that will predict the behavior--nothing ever happens without warning, it just happens so quickly we often miss it. If you happened to have video of it occurring, we'd be better able to give advise as to the possible cause and suggestions for altering the behavior.