The doctrine of Once saved always saved is a lie straight from hell, and is a license for sin and immorality in a believers life!
There is enough doctrinal proof that speaks of a "great falling away".
2Th 2:3 Do not let anyone deceive you in any way, because that Day will not come unless first comes the falling away, and the man of sin is revealed, the son of perdition,
That term "Falling away" means apostasy, Which means defection from truth, Falling away or to forsake.
Lets use a little common sense here: You cannot defect from something you were never a part of. For example, you cannot defect from a country unless you were a citizen of that country. You cannot forsake a marriage unless you are married, nor can you forsake a relationship with God, unless you first had one.
There are a host of other scriptures, but I will post this link that will put it into better words.
http://www.evangelicaloutreach.org/everyNTbook.htm