first off is your first dog neutured ? second off does he have his shots ? i ask because bringing a new dog into the house can have health issues , second off slow and steady, it takes time and patience, it sounds like hes just trying to show his domance that hes pack leader, the more you defend the other one the harder its going to get. unless theres blood let them be. just closeley monitor so neither one gets hurt. althought i could be wrong but to me this is what it sounds like