I don't know if this will help or not. We have a shep/rottie male mix. He is now 2 years old and about 7 months ago he decided that he didn't want to listen to me anymore. I am the one that has been home with him the majority of the day and pretty much trained him to do his tricks and thought I had him obediance trained. (at least to the best of my knowledge.) After talking to the vet they recommended that we speak to a dog trainer. He is now in obediance training at the age of 2 for modified training. According to the trainer he lost respect for me and he now feels that he is the dominant one over me. What he does is when I tell him to do something he will grumble and growl and he has even went as far as lunging at me. This is a 110lb dog compared to my 120lbs. Not much of a difference. He would do the same thing with my fiance but not to the point that he was with me.
The best thing that you can do is talk to a very well recommended dog trainer in your area. Your local vet should be able to give you a name and number. Mac has been going for about 4 weeks now and we already see a difference.
It will take time and patience but it can be done. I hope this helps.
Sherryvic