My concern is that the overterritorial Chihuahua comes busting out of a door while I am walking my 100-pound Labrador and then gets a hold of his leg. He has a peaceful demeanor, but there are limits. Or the unsocialized creature gets a hold of my ankle while walking to the park without dog.

There's nothing good that can come out of this. The likely outcome is a dead small dog and a vet/physician bill.