I am new to this forum so apologies if this question has been asked or answered before.
I have a very good natured, 14 month old GSD. She is well socialised, trained and exercised regularly. She goes to the dog park regularly (at least 4 times a week) and for long walks, bike rides every day. She has never been aggressive towards humans or other animals.
At home she is allowed to roam both inside and outside the house. As I work from home, she generally spends the vast majority of time indoors with me just sleeping on the couch . Our front garden is completely fenced off and so visitors press a doorbell to alert me to the fact that I have parcels etc or to let them in. While she has always responded by running out and barking (when she hears the doorbell) - she has always been quite respectful in that once she realises that I know them, she generally lets them in without a fuss.
Just recently however, I had a friend show up (who was a scared of dogs) and I went to the gate to let him in, and she was snarling quite viciously. I held her by the collar and let him in but she tried to lunge towards him I told her off and left her outside until she had calmed down. He was obviously quite shaken! I let her in the house after about 20 mins and she was fine (with the guest indoors as well). Following this incident I have noticed that she has become very aggressive at the gate. Outside she is fine and super friendly to all, but obviously I want to be able to get mail, talk to tradies etc without my huge dog lunging at the gate.
Does anyone have any suggestions as to how I could train her to stop doing this?
Thanks in advance!