When I was in the dog biz in the USA I found Staffys to be a bit belligerent and often dog and sometimes human aggressive. Here in Australia, they are much more common and most of them are the sweetest things you have ever met. I think you can keep most any breeds together, depends on the individual animals, how they are introduced and handled. I have always had Akitas and Bouviers, akitas in particular are famous for their dog aggressiveness, however mine were never allowed to exhibit that behavior and do not show the tendencies, they lived with cats and birds and small dogs and big dogs and were fine. I was always careful though with strange dogs outside of my environment. Some people here do not like Cesar Milan (I think he is great) but regardless of your feelings on his training techniques, it is amazing the way he runs that pack together and they all seem to get along just fine. Read his books or watch his shows to see how he does it.