Once saved always saved???

I thought that was a very good question. I have always believed that once a person confesses that they believe that Jesus is the Son of God, & rose from the grave & accepted Jesus as their personal Savior, that they would ALWAYS be saved. No matter what. That has always been my belief, no matter what they do, or if they get off the path of God. Because I believe it says in the Bible that is the criteria for salvation. I'm just wondering if there is any indication in the Bible where it says that once those things are done, that if a person commits some haneous (sp?) sin, that God will take back the fact that they once confessed that Jesus is the Son of God, & their Savior, etc, etc. My belief is that once that is done a person is saved, & then based on the works that they do through God, then their treasure is stored up in heaven for them when they die. And if a person becomes saved, but say, years later, get away from God & go back to a previous lifestyle, etc, then maybe they will not get as many treasures in Heaven, as would somebody who stays close to God would? I guess I just find it hard to believe that God would clearly state what has to be done to get into Heaven, & then take that back, & once a person did that, but they stray from God, then God will change His mind, & say, no, this person should go to Hell? Any other feedback, suggestions, on this?