The Shield of Faith, along with the belt of Truth, breastplate of righteousness, helmet of Salvation, shoes of the gospel of peace, and the Sword of the Spirit, which is the Word of God, work very well against exterior attacks. (See Ephesians 6:11-19)
The internal ones need to be cast out, which is what Jesus did, and Christians can do, although it is not done often. Here is a video on the subject of demons in Christians, and what can be done to remedy the situation. The speaker and minister is Micah Stephen Bell, of Key Ministries, in the Dallas area.
https://www.youtube.com/watch?v=229AWOETxKU
Good grief ...