How should I protect myself?

I do not like my step dad. Something about him just dosent seem right. He has done somethings to my mother that are to the extent to make me question his motives. I want to know if I should start sleeping with a knife under my bed incase something ever happens. I already lock my door at night and sleep with my cellphone next to me so if I need to call police I can. He has never put his hands on me but he still seems like he has problems. Advice? I'm 17 by the way.