Rosa is just over 2, she is the working dog.
Both live in the house. Family environment. 2 kids 14 and 11.
Rosa is well trained: heel, come, sit, stay. Not at all gun shy, good bird instinct. Her retrieving is excellent on dummys, getting there on birds.
So far obedience has never been an issue. They never run off even though the garden is not fenced and we are surrounded by fields and forest.
Both dogs are excellent "alert" dogs...plenty of loud barking as anyone approaches our quite isolated house.
So much for the background.
In the last 2 months Rosa has become increasingly aggressive, so far limited to unpleasant growling at strangers of all shapes and sizes. Human and dog alike. It is not all the time, it is not always the same people or the same place or the same dogs.
Last weekend she did get quite nasty with a friend's dog (which had the good sense to run away, so no harm done).
We have not let such behavior go unpunished. So far we have grabbed her neck/muzzle and given a good shake while talking/shouting very sternly. I have even turned her onto her back and had my face right in hers while growling "NO NO NO" myself so as to make it 100% clear who is the pack leader!
Like I said, so far no harm done. However I am quite concerned that she might go for somebody quicker than we can get to her. Keeping her kenneled, leashed or tied up is simply not an option.
I need a training/behavioral solution.
There is such a wealth of knowledge here...ideas please?