Sorry to hear about your bad luck!
I am prone to such things happening to me, and I can get distracted pretty easily. I decided long ago that if I can help it, I will never set something in a place where I couldn't handle forgetting it. If I set something down, I set it where it won't get dumped, run over, or fly off. I know a girl who set her expensive violin down behind her car while loading it up, forgot it, and ran over it.
Here's another great example... someone (and his family) once came to stay in my house for a couple weeks while in the process of moving, and forgot his loaded .38 special. 3 weeks after they moved out, my 7-year-old found it.