How do I get my roommate to NOT use my bed?

Long story short, I am going away for a few months. I have been looking for a subletter but have not had much success. A few of my roommate's friends have expressed interest, but have been dragging their feet to actually give me a yes or no answer. I have a feeling that he is just going to let them use my room rent free. I don't accept that. How can I rig my room to make it unliveable to make sure that he is not letting out my room? Our rooms don't have locks and my landlord won't let me install one. Thanks!