mmmm sounds like a dominance issue really. Like one of them is pushing boundaries and the other one is having to work very hard to stay on top. Often in every relationship one of us is the boss.... nicely put. I'd like to say that DH & I are equal, but in reality in the home.. I'm the boss (not really something I'm proud of ). I can um.... argue my point until I get it my way. He doesn't really care about those things as much and would rather keep the peace. So its perfect because we don't fight about much. BUT if DH sudden started to assert himself more and argue with me over my little issues (like the rubbish not going out, or something silly like that) it could cause major riffs in our relationship and I would feel angry because he's changed and he would be angry because he wants his way... etc etc. Now I'm talking about silly things like rubbish etc, but as women we all know this adds up in the end.

For dogs its the same, an example is walking through thresholds. Gates, doors and even barriers like arches etc can cause rifts in their dominance. Who is closest to the person... mainly the boss person. Who gets their food first... what order are they fed? Are there more fights if one is fed before the other... I'm talking seconds here.... the seconds it takes to move from putting one bowl down to the other....?

Main causes of fights in family dogs: Food, order of food, thresholds, people, height. Whoever is the tallest has an edge on the dominance issue.... but beds etc can cause issues as well if you have a dog that is threatening the order of the house.

Now, this is an older way of thinking about their behaviour... family packs etc... they change over time in other houses and in wild packs. Generally the boss is always the boss and the rest of the pack fights and argues their ways up and down the ladder.... so there isn't always the same dominant dog all the time in a pack/family. But when they are rearranging, often there are blues getting there.

You can try to encourage the boss to stay the boss....by making sure he/she goes through the doors, thresholds, eats food etc first. But you need to be sure who the boss is before doing it.