At 15, kids think that they are indestructible. No matter how many stories they hear, they will feel like this is stuff that happens to others, not to them.

What you should do is talk to him honestly about the reasons you feel he should wear the harness and let him know that you trust him to do the right thing.

From that point on you’ll have to trust him because no matter what you tell him he will do what he will do when you are not there.

Good luck!