Silkies can be very territorial when it comes to other dogs. I think the main reason is that they don't think that they are dogs and the sight of another dog reminds them that there is a possibility that they are not human. They must get the vermin out of their sight in order to restore their general view of the universe, with them at the center, of course!

Silky Terrorists usually get along with other silkies, but your best bet is to get a female of any breed. The males tend to defend their "turf" quite vigorously from other males.

There are a few rules that can be followed to help Angus feel more comfortable with a new dog. Introduce any new dog slowly (over the course of days or weeks if possible) and only give the new dog attention and coddling when the Silky Terrorist is off doing something else. Silkies are also prone to jealousy, as are most lap dogs, and premature acceptance and attention in their presence will exacerbate the problem. Keep the new dog crated when you are not home if Angus is allowed free reign. This will show Angus and the new dog that the new dog is of lower status than he is. Always feed Angus first: make sure the other dog does not eat until Angus is completely finished. He obviosly knows that he is top dog and will take offense to any other dog that tries to eat before or at the same time he does. If Angus sleeps in your bed, do not let the other dog sleep there until Angus lets it. This is a status thing as well and eventually, if he learns to like the other dog, he will allow some leeway to the other dog. Unfortunately you will relegate the new dog to second-class status, but this will be necessary to keep the peace.

Oh, and submission roll Angus every once in a while. If he does not allow any other dog to live in your house, he belives that he is the Alpha dog. By getting rid of the other dog you are telling him that if he misbehaves, he calls the shots and you will bow to his whim. Submission rolling him will clearly show him that you, not he, make the rules. If he fights you, you know that he thinks of you as a subordinate in your family pack! (Just don't roll him in the presence of the other dog until after he accepts the other dog. You can roll the other dog in his presence, however.)

Good luck and I hope it helps!