To keep skunks away
When we go camping we put moth balls in 1 pound coffee cans, punch holes in the top (plastic) and put one in front and one in back under the trailer. We have never smelt the moth balls in the trailer. I also have put the moth balls in a wood pile away from the dog, or hung them around outside. It seem to work pretty good.
PS Please don't put them where children or pets can get them/ In fact, I would not put them down during the day only at night in the campgrounds.