Second, there is no need to carry around plastic bags of the food you ate. If you test positive for contaminated meat, you should be able to go back to where ever you got the meat and any random sample should also test positive. If that doesn't happen, then you must be one seriously unlucky person to have eaten the only piece of contaminated meat.
I’m not going to argue Bert’s case with you, because as I said before, I mostly agree with you. But I’m not so sure that in third world countries the chain of custody is as transparent as you make it out to be. If random meat samples from a town of Mexico vary widely in their CB contamination, then it may be that the butchers have multiple sources and/or the sources themselves vary widely in comtamination levels.
It actually would be very hard to do because it is likely you would have to synthesize the excreted metabolized molecule of clenbuterol as well and then plant it. And second, no lawyer would do this unless they wanted to get disbarred and go to jail.
The latter argument can easily be dismissed. The rider or his medical advisor would do the spiking, not the lawyer. The former argument is a better point (not the excreted metabolite, but any metabolites produced from enzymatic action on CB in specific tissues), but of course it would require a whole new validated testing system in place. I doubt that the metabolite profile of CB in muscle is even well known, and it would certainly change over time. In any case, there would have to be a specific criterion that would set what is a possible ratio of CB to some metabolite. They don’t test for these other metabolites now, and it would not be a quick or simple matter to set up a test like this. I really can’t see WADA doing it just to guard against spiking, when there are other ways to get at the underlying problem.