I've be using a natural rock deodorant for several years now, and I highly recommend it. I found my first crystal rock deodorant at a health food store, and it lasted almost a year. The second one was on sale at one of those organic and natural grocery stores. It was advertised as the best natural deodorant, although customers seemed a little reluctant to try it.
When I used commercial deodorants, I would shop for a replacement about every three months. I'm still using the same organic rock deodorant I bought a year and a half ago. I still sweat when I work outside or go to the gym, but I'm not offending the people around me.