I have them recite the rules back to me at least three times during the session.
1. Treat all firearms as if they were loaded.
2. Never point the gun at anything you aren't willing to destroy.
3. Don't put your finger on the trigger until you are ready to fire.
4. Be sure of your target and what is beyond it.
You need to know these rules and follow them always.
The best safety is the one between your ears.
Remember, You can “never take it back”