Civilian gun ownership doesn’t stop counter-revolutions. If the people are motivated and organized enough to mount an armed defense of the revolution then the conditions would not have arisen in the first place to where that defense is necessary. Counter-revolution happens when the accumulation of errors made is so grave that the people are too demoralized to fight the reactionary takeover.

The Soviet Union didn’t fall because the people lacked weapons. The Soviet army had plenty of weapons, why didn’t they stop it? Why didn’t the security forces? Power doesn’t come from simply “occupying the halls of power”, it comes from the consent of an entire apparatus of state, which in turn rests on having the consent of at least a certain part of the population and the compliance of the rest.

There is this Chinese documentary that analyzed and summarized the causes of the fall of the Soviet Union that might be interesting for you to watch if you want to understand the conditions that were present in 1991 which made it so that, weapons or no, the population was no longer willing to defend the system. Preventing counter-revolution can only be done by not letting things get to that critical point in the first place.