How do I get my man to choke me???

I ask him all the time, he says that he doesn't want to leave marks on me and that if he ends up doing it he's scared he's gonna get too carried away. I tell him not to worry about any of that but he insists and he thinks I'm too fragile. I never get mad at him over it and I don't act too serious when I talk to him about it. Should I be more assertive? Should I be like "im not gonna have sex with you if you don't choke me" lol🤣