We adopted our Boxer, Winston, from a local rescue, 3 1/2 months ago and he has now developed a terrible aggressive behavior. He is about a year to a year and a half old. He gets along great with our 3 year old pittie, Kai, and is great 95% of the time, but the aggression seems to be getting worse. He sits in our front room looking out the window and if anyone walks by he start barking and lunging at the window. Then if you try and get him off the couch he lunges and tries attacking. He is the same way if the door bell rings, we can't get him away from the door without him aggressively trying to bite us. We have a trainer we were using for Kai, but due to COVID we can't get into see her and she hasn't been able to meet Winston yet. My family has always had boxers and I haven't ever experienced this level of aggression before, so we are kind of at a loss. We don't know what the best way to correct this would be. We tried purchasing a baby gate so we keep him away from the door and away from the front room, but he has learned to just jump on the gate to push it over and then we are back at square one. We try to reward him with treats when he comes when he's called, but it's like he has this ball of fire that he can't control, even if it's me or my boyfriend trying to get him away and to calm down. It's definitely gotten worse over the last 3 months.