Depending on his age and the circumstances of how you acquired him, most of the time insecure behavior is because the dog feels he is the pack leader, and he is insecure with this role. I recommend crate training to help establish boundaries, and to give him a "safe" den where he can feel more comfortable. Teaching him tricks, and taking him to public places where he can meet other people also helps. You need to make sure that you are the pack leader, and that you are emitting stable and leadership energy. For more specific types for your particular dog and situation, go to liveperson and ask for Maya Moon~