We have a four month old, beautiful black GSD, unfortunately since this little guy has come into our lives, our two year old female GSD has become quite aggresive. When people come to our home, she lunges at them and barks quite loud when they leave. Yesterday she ran through the electric fence after the UPS delivery man and tried to attack him. I can't figure out what to do and I am really stressed about this. This cannot escalate, it is becoming a safety issue for both the dog and anyone entering our property.