Diatomaceous Earth

http://www.permaguard.com/items.html

http://www.dirtworks.net/Diatomaceous-Earth.html

http://wolfcreekranch1.tripod.com/de_retailers.html

http://www.greenharvest.com.au/pestcontrol/diatomaceous_earth_prod.html

http://www.earthworkshealth.com/products.php?

http://wapedia.mobi/en/Diatomaceous_earth

http://en.wikipedia.org/wiki/Diatomaceous_earth

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A couple of articles from The Whole Dog Journal about flea treatment chemicals and non toxic treatments;

http://www.apnm.org/publications/resources/fleachemfin.pdf

http://www.homevet.com/petcare/documents/fleacontrol.pdf