Question: Suppose I want to reduce risk of a circuit breaker malfunctioning and failing to disconnect a shorted circuit.

What if I install two identical breakers sequentially (one after another) so that if one of them fails the other one steps in and disconnects the circuit? Is there any problem with such installation?

Answer: 
Most generator manual transfer switch-over panels require you to do just this. The wire coming out of the breaker and going to a load (normally) is disconnected and channeled over to a second panel with another breaker and then then the biter-end coming out of the second panel is tied back to the load. In short, two breakers in series.
Two breakers in series would reduce the risk of one failing in a way that stays in a closed (conducting) position. But modern breakers today have an extreme low risk of this happening. If I were that paranoid, I'd put a breaker and a fuse in series. But I'm not.