Is there anything that is least noticeable that I could do to my car so it will not start

I’ve been noticing for the past two weeks my gas has been looking low every morning when I go to work. I asked my family if they had went somewhere and that night and everyone said no. So I put some whole peanuts under the back wheels and sure enough they had been ran over that morning. So I asked again and of course no one knew anything. So I got my sons deer cam set it up and went to bed. That morning I checked the photos and to my surprise it’s my loving boyfriend that lives with me and has a key. I don’t want to press any charges on him but I to want to make the car is immobile. I was wondering if there is anything that is least noticeable that I could do before going to bed so it will not start? If so please let me know. Thanks a million and God bless.