Personal space aggression may be the result of the dog worrying about a person or dog acting in a predatory way towards them or they may be possessive of something and try to defend it.
Correcting such behavior requires you to be prepared with your training tools and knowing, what it is, that you want your dog to do, instead of that personal space aggression.
I have seen small toy dogs, though this is not unique to small dogs only, who have been on the couch with their owners, being caressed and loved on, and when another person tries to sit down, they growl and then the owner pets the dog as it is growling. This is basically telling the dog, that the growling is a behavior the owner likes and the dog will want to do it more.
I know, i have said this many times before, but I like to do place training with my dogs from a very young age. It is such a great skill to teach, because it solves so many problems. You are teaching your dog, where you want him to be and what happens, when he comes off the raised dog bed. You are also teaching your dog, what happens, when he is obedient and stays on his place.
Longoriahaus Dog Training is a dog training service in the Kingwood, Humble and Houston, Texas area. Longoriahaus Dog Training can help you raise a happy and reliable dog.