I have similar issues with Bandit. When he's familiar with people and dogs he is incredibly friendly, but when it's a stranger or someone he percieves as a threat he's incredibly territorial and even aggresive. The water bottle helps with the barking at first if it hasn't escalated too much as well as the pennies in the can for barking. We've been training with Bark Busters and that's helped, and he goes to DayCare once a weeek and that helps with his socialization with other dogs, especially new ones. Good luck in training and let me know if you come across something that works
