Behaviour

Question
I have a 5 year old male Aussie. Recently I acquired another dog that is requiring alot of my attention. Since acquiring this other dog, my Aussie has attacked the other dog 3 times. This is very out of character for him, as he is usually very loving and non-agressive with other dogs. Are there any recommendations for how to deal with this type of behaviour from him?

Answer
What gender, age, and breed is the other dog?  What is the other dog's socialization history?  When you say "attacked" do you mean blood was drawn, or not?  Aussies can be extremely territorial and possessive of their own people and places.  So, even though your dog is fine with others off the property, he may have a different view of an interloper.  I never like to try to change a resident dog in favor of forcing a relationship with a newcomer, unless the disagreement between them is fairly benign, but you have used the word attack, and have said that there have been multiple instances.  Is this second dog really worth destroying your relationship with dog #1??? While there may be hope here, I would need to know much more about the situation, hence my questions.  Please feel free to engage in follow up discussion.  Recommended reading: "Feeling Outnumbered?" by Patricia McConnell and http://www.shirleychong.com/keepers/archives/many.txt.