First you have to understand a little bit about the breed. While they are cute little dogs they are also members of the Spitz breed of dogs. This means they can be very independent, very headstrong and in their world everything will belong to them.
Even at only 12 weeks old this pup has established himself as the leader in the household. You will need to take back that leadership role. One thing that comes to mind that you can try is the NILF program. This stands for Nothing In Life is Free. A Google search will lead to many links about the program. If followed the program works but only if you and everyone in the household makes a commitment to have it work. Basically what happens is the pup must perform a simple basic command before he gets anything from you. This will mean greets at the door, pets, hugs and even food. Once he does what you ask even if it's just SIT... then you reward him.
Another thing to try is leash training. This will also help establish some limitations. Keep the leash connected to his collar. This will give you or someone else something to grasp when the pup misbehaves which in turn keeps you safe from bites. Above all, do not push him away to get him to stop, he thinks this is a game and will only continue.
Lastly... how much excercise does your pup get? A tired dog is a happy dog and your pup could simply be bored to death with a lot of pent up energy. He should get at least two very long walks a day or plenty of playtime in a fenced in area like a backyard or a park to burn off excess energy. These types of dogs have an over active mind and need plenty of stimulus to keep them occupied.
All is not lost with your little pup. By following some of above or any modification of it and you will soom have an extremely loyal dog who will soon understand that you are the leader.
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Dogs are not our whole life, but they make our lives whole.
PHMax