Super comment @jzen, thank you.

Well, be careful though. It is not because a product is 'natural' that it is not toxic or eco-toxic. For example, I use Alun stones as deodorant under arm pits. But I do it very seldomly (a couple of times a month). Although it is natural, it contains al3+ salts which are carcinogenic!
I also notice that since I stopped using deodorant, I do not need it, and I don't stink!

For all alternatives you wish to use (like borate), Look for and Check the MSDS (material Safety Data Sheet).
For example Borate tetrahydrate (Borax) appears OK, but its acid version is pretty crap... So be careful.
Borate: http://www.sciencelab.com/msds.php?msdsId=9924967
Boric Acid: http://www.sciencelab.com/msds.php?msdsId=9927105

Check sections 11 and 12 for more detailed toxicological info.