If I believed, as you teach, that once saved; always saved, couldn't I just live any old lifestyle that I wanted to?
Answer: Yes, I suppose that you could. However, you seem to be suggesting that if you did resort to some kind of sinful behavior that it would go unnoticed and unchallenged before God. Be not deceived my friend, ".whatsoever a man soweth, that shall he also reap."
When a person trusts Christ as their Saviour, God becomes their Heavenly Father. The Bible says in Hebrews 12:6, "For whom the Lord loveth he chasteneth, and scourgeth every son whom he receiveth."
Think of it this way: When you were a child no one forced you to go home at night, but you did. Why? Because you knew that if you didn't go home, you would have to answer to your father. Well, the same reasoning compels the child of God to behave properly.