Basic training helps tame a territorial dog. If your dog is in the habit of refusing to share or drop a toy, train him with the ‘drop it’ command. Offer a treat, and give it to him when he puts the toy down. If he understands the ‘sit’ and ‘stay’ commands, you can use these to make him stay in the same spot when he starts barking when the door is knocked as you go to open it. If he is in the habit of barking at strangers over the fence, teach him the recall command, so that he leaves the fence and comes to you. You can also use the ‘stop’ command to make him stop barking.
Make it clear to your dog that he gets nothing for free. If he wants to go for a walk, make him sit before putting on his leash. Before he gets a treat he has to sit. Dogs get territorial when they think they are entitled to things, but when you make it clear you are in control, the dog will be less territorial and demanding. Make sure you stick to a routine on a daily basis, so the dog is assured of a meal or a walk at a certain time daily. A fixed routine eliminates the need to horde things to sustain him in future.
In a household of more than one dog, provide toys for everyone so that they don’t feel the need to fight for the few available. Also, keep triggers to the minimum. If your dog barks at strangers for example, make sure you keep him indoors and away from the fence until he learns the basic commands you are trying to teach him. As he gets used to the training, let him out into the yard gradually to see if the commands are working.
Make sure you teach basic obedience on a daily basis so that the commands become second nature. The refresher trainings won’t take as long as the initial ones, so five minute trainings should suffice. As with any negative behavior, you have to give your dog time and be patient with the trainings. Be consistent too, to avoid confusing the dog.
Territorial Dogs: How to Control the Behavior