we have recently taken on a border collie aged 4 because one of our other dogs died and we wanted company for the other.
When we went to see him he growled a little and we were told that he sometimes did that to strangers but didn't bite. We walked him with our dog and he seemed lovely, they played together and he was good on the lead.
Now we have got him home, he can be fine one minute and then for no apparent reason starts growling, which will intensify if you don't stop whatever it is you are doing. This includes stroking him, talking to him, looking at him. Even offering him a treat.
Just as quickly it can change back again and he is all over you.
He has only been with us a week. Does anyone have any advice to offer?