YES! Demons are real! I fight them in church. The only way to get rid of a demon is to rebuke them in JESUS' name!!! There are people I've seen in church who are filled with evil spirits. They can only be ridden of if they are rebuked in the name of Jesus!
Demons are a very real threat, but to have trouble with a demon, you have to do something to invite it into your body. Salt will not help you. If you are truly having trouble with a demon, consult an exorcist. If you're curious, There may be one at your local Catholic church that you can talk to. Vatican rules state that there must be at least one trained exorcist in every parish.