I actually really disagree with the idea that dogs in any way, shape or form see humans as their 'pack' and always try to offer a different perspective as I think it makes for a far more productive and happy relationship with dogs. I've never seen a jot of evidence that my dogs think I am a giant dog in their pack at all! Indeed it is well documented that they recognise people as people (they are far more adept at this than wolves!) and they will respond to people to the degree that they show confident, capable leadership. If you want proof, just consider what your dog does when it sees a cat when on a walk, and when it sees a dog. Most likely, it is interested in meeting and greeting the dog, and wants to bark at and chase the cat. It doesn;t see the ca as part of its pack either -- even cats it lives with. Dogs see cats as cats, people as people, to be respected or not dependent on the relationship and obeyed to the degree that the human has taken any time to teach the dog wanted behaviours. (Punishment is NOT training, but I'll come back to that).
Dogs are also smart enough to understand a LOT of human body language which in itself indicates they don't see people as part of their pack.
So please, the best thing anyone can do regarding their relationship with a dog is remove the words 'pack' (when it comes to including people) and 'dominance'.
With this dog -- it sounds like there's a pretty basic situation here of some upsetting of a routine and perhaps some unhappiness at a shift in attention going to your girlfriend -- and your male dog may feel he needs to make a statement about the fact that the house has been the territory of the two of you (hence the marking) and/or he is also feeling anxious about why this new person has suddenly arrived on the scene (hence the marking and the overexcitement). And dogs mark to say 'Hi!' -- urine is full of information for another dog -- that's why they pee in front of each other and all run over o sniff it. He may just be greeting her and offering her his version of a calling card.
He *isn't* 'showing his dominance' or asserting his pack leadership over your girlfriend. He would be showing the same behaviours if you had a baby, brought in another dog or a cat, or even, moved into a new house alone with him -- dogs urinate for a huge range of reasons and will jump on people with excitement. But not all dogs express these anxieties or overly friendly behaviours that you are finding a bit rude -- the fact that he does indicates there are a few things you need to do:
* one, if he isn't neutered, consider doing this as for the majority of males, this alone will stop indoor marking, and excessive marking indoors or out. It will also lower his territorial instincts which will help the anxiety the defensiveness, AND the marking
* two, make sure you aren't neglecting the dog during the time you have your girlfriend around. Chances are you might be spending a lot less time around home with the dog if you are spending more time with a girlfriend -- so there could be a couple of knock on effects. He may well scent her on you when you return from being away longer periods and associates her smell with some anxiety and unhappiness (you not being around as much).
* three, *training*, the most important of all. He is acting the way he does because he either is a bit insecure and uncertain, oris trying to be too enthusiastic and friendly -- but either way, lacks self control and the knowledge of APPROPRIATE behaviours *(which YOU have to teach him!
). Doing a good rewards-based obedience class, doing agility, training tricks, in general, spending concentrated and productive learning time with your dog brings you together and also boosts your dog's focus, confidence and self control which in turn makes for a less anxious, territorial, lonely, threatened, bored dog -- any one of which may be contributing to the current situation. At the very least, you should have a dog trained well enough to 1) stop when told to stop marking and 2) refrain from jumping on people. But learning this takes time and effort from the owner -- the dog can't figure this out alone. He needs to have someone setting out the wanted behaviours and rewarding them. In short: NOT 'correcting' (read: punishing) bad behaviours in a negative way, but REWARDING the behaviours you want.
Consider that the word a dog hears most is 'no'. Just as with kids, constant punishment or correcting for unwanted behaviour does absolutely nothing at all to shape the wanted behaviour and you end up with an anxious, unhappy, fearful dog whose unwanted behaviour may well intensify because he has no idea of what is wanted. Through a good rewards-based (eg positive reinforcement) obedience class, your dog learns what is desired and you learn how to deflect an unwanted behaviour towards a wanted one.
So you have a project on your hands!
I recommend buying one of Dr Ian Dunbar's books on working with dogs, checking out some of the training documents on
www.deesdogs.com, and some of the great training articles here:
http://www.diamondsintheruff.com/behavior.html. You will find several articles on the two websites dealing with the behaviours you mention but having a good training manual at home, such as one of Ian Dunbar's, is very useful.