I take along a small container of moth balls and place one along the top outer edge of my car every foot or two. I know one other long-time Sierra hiker who has been doing this for years and swears by it. I also have never had any problems using this method, although I am also careful in what I leave in my car, etc. as mentioned by others above.

CaT

If future generations are to remember us with gratitude rather than contempt, we must leave them more than the miracle of technology. We must leave them a glimpse of the world as it was in the beginning, not just after we got through with it.
- Lyndon Johnson, on signing the Wilderness Act into law (1964)