It is not easy to guard against fermentation of wheat or other grains. Even washing can be a problem, as is outlined in this page.
Rabbah said: A conscientious man should not wash [corn]. Why particularly a conscientious man: even any other man too, for surely it was taught: One may not wash barley on Passover? He says thus: He should not wash even wheat, which is hard.
And yet, wheat has to be washed in order to make the fine flour needed. In fact, the argument is made, specifically because of the command to “guard” the grain must be washed:
Raba said: It is obligatory to wash [the grain], for it is said, And ye shall guard the unleavened bread. Now, if not that it requires washing, for what purpose is the guarding?
Since grain can only ferment if there is moisture on it, there would be no guarding without washing! Or maybe it can be applied to other stages?
If guarding for the kneading, the guarding of kneading is not “guarding”, for R. Huna said: The doughs of a heathen, a man may fill his stomach with them, providing that he eats as much as an olive of unleavened bread at the end (of the first night of Passover). [Thus] only at the end, but not at the beginning: what is the reason? Because he had not afforded it any guarding.
So, “guarding” is saving for the end? Or others:
Then let him guard it from the baking and onwards?
Hence this surely proves that we require guarding from the beginning. . . .Yet even so, Raba did not retract. For he said to those who handled sheaves, Handle them for the purpose of the precept. This proves that he holds [that] we require guarding ab initio, from beginning to end.
Thus the custom some have of a special “shemurah (guarded) matzah” – a matzah used specifically to fulfill this commandment – guarded, or watched, from harvest to baking that no water or moisture touches it until moments before baking. Not very palatable, but useful for its purpose.