Good point about hair... hair actually absorbes and stores all drugs that you ingest - thats paracetmol, calpol, gear, ectasy, heoine - whatever you take. There are drug tests run on horses using mane/tail hairs to check for doping and it can be done fore humans just as easily, however, isn't obviously a prefered method as some people, especially men, have quite short hair... may only be a few weeks old, so pretty pointless for long term checking...