and what happens when some want to guard production to gain personal advantage?
Communism on the surface was a great idea, problem with it was it ignored the fact that people were involved in it, and that people will always strive to better their situation.
This is why Anarchist-Communism is a flawed idea as it denies the human factor of the equation.
Although I'm not a communist myself, there are several things wrong with what you're saying.
First, not all communists are collectivists. William Godwin would be one example, but there are also those who think that "from each according to his ability, to each according to his need" is an expression of individualism, since "ability" and "need" are both self-determined.
What happens if some want to guard production? If the means of production they're guarding is their own, that's perfectly fine. If the means of production they're guarding is not their own, but belongs to someone else (or possibly belongs to the collective), then that's not fine. I could just as easily ask what happens under anarcho-capitalism if someone wants to guard the production of somebody else's things.
Besides, you seem to be under the impression that anarcho-capitalism and anarcho-communism are the only possible forms of anarchism. They're not; many anarchists are anti-capitalist, but pro-free market. I myself, for example, consider myself a mutualist.