protective, aggresive, or jealousy

Question
I recently got a new roommate who has 2 large dogs. Both of them are large
adult mixed breeds. One female, and one male, ages 4 and 6. I have a 6 year
old male chihuahua. He is used to being the only dog and is having a hard
time adjusting to the new ones. He growls and snaps if they walk by him
inside the house. If they are all three in the yard, there is hardly ever any
aggressive moments. Everyone smells each other and seems to get along
perfectly. The chihuahua did try to mount the other male dog yesterday. The
aggressiveness is geared mostly towards the larger female. She does growl
back and it makes me very nervous to try and leave them unattended
together. We have began taking the large dogs on long walks. And before the
new ones arrived, we took, and continue to take the small one on walks as
well. We were thinking of trying to walk all three together as soon as we are
confident we can keep control over them. Thank you so much for any help
and advise. I just want us all to be able to get along and live in peace and
safety.

Answer
The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at http://www.dogsbestfriend.com/ For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm

All 3 dogs need to understand you and your roommate are in charge and expect them to maintain peace.  Having them all spay/neutered should help.  

You may want to crate your dog when you aren't around to protect it.  A dog that has not been crated since it was little, may take some work. Start out just putting its toys and treats in the crate. Praise it for going in. Feed it in the crate. This is also an easy way to maintain order at feeding time for more than one dog.