It is possible to cast Satan out of your life. Binding him from having power or influence over you directly just as he will be bound in the Millennium. This is one of the simple unspoken lessons of the Temple endowment. Satan can still effect you through others, as he did with Christ and the apostles, but not directly.
He gains power when you have faith in him. One of his greatest tools for instilling faith in him is fear. The more fear we have for him, the more faith we have that he is more powerful then we are. But the truth is that we have everything he has and more. We gained every blessing a spirit can gain before coming to earth. He on the other hand was cast out. Where his progression ended, ours continued. Now we have spirits and bodies. We have more power than he does!