Compromise and get a goose.
In ancient Rome, the city was guarded at night by geese.
As for a guard dog, you have to get extensive and expensive training for that. But maybe you just want an alarm dog - one that will bark at an intruder, or even defend you if the intruder attacks. Most dogs will do that instinctively, and even a fairly small dog can be an effective defense.
A dog, especially if you get it young, will generally follow your lead as to how to treat other family pets. The way I introduce them is to tell the dog that the duck [or whatever] is a special gift for HIM, that it is a very cute puppy, and he should treat it kindly. BTW it is easier to convince a female dog that another pet should be treated like a puppy.