Thanks for all the great suggestions. I am currently keeping them separated while I am gone and keeping a close eye on them otherwise. The problem is that Penny Lane also suffers from separation anxiety and goes a little nuts when she is left by herself - she was fine when she and Leo were left together. Things seem to have settled down a bit, but I am still a little nervous when they get too close to each other which I am sure I am telegraphing to them It is definately fear aggression with Penny Lane - she growls and shakes at the same time. I just got a little freaked (okay a lot freaked ) when Leo turned so vicious on her. Leo has never acted that way before. I am going to enroll her in obedience classes and keep working with her socialization. Wish me luck!!!