Immediate help needed! - aggressive 3 year old

[Forester]

I have lived with my boyfriend now for almost a year he has a 3.5 yr old German Shepherd x who has becoming increasingly aggressive to my 8 yr old Mountain Feist. For no reason at all, just today she attacked my 26lb dog for no reason. Thank god I was in the yard! She turned on him.. no reason at all and lathched on to his neck (which was basically half of his neck in her mouth). She didnt puncture his skin but if she had.... no doubt she would have killed him. It took about a minute or so of kicking and punching to get her off of him. i dont know what to do. There were no signs.. no change in behavior, no hair raised, she just turned and bit him. I have worked around animals to notice signs and there was nothing. I just dont know what to do... any advice would be great. Im still really upset about but its just not fair to any person or animal in this situation. Sorry, still really upset right now so sorry if its all a bit jumbled.

[LoveEcho]

If I recall correctly, you posted the same exact problem on another thread under a different username... I understand that thread turned into an argument over pos/neg reinforcement, but there was some advice offered on there prior to that. Did you take any of it?

You can't really say there were no signs, because this is apparently not the first time. You know she was prone to it. Management and keeping them separated needs to be step number one, before anything else.