loosing keys

My cousin is terrible with house keys. He recently came to stay with me. Before he was staying at his parents house. After coming to stay with me, this is the 3 time in a single month he lost the key to the flat. Lucky that I am around I am able to open the door with my key. I keep telling him to properly tuck the key into his pocket. But he says it falls off when he drives on his motor bike. I cannot understand that how others are not loosing it when they drive around with many things in their pocket. Any suggestions and advise that i can suggest him.

Please help. I am quite distressed about his behavior. 😭