I have to disagree about this one. Cars, sure: we try to engineer cars to protect people better in crashes, we invent devices to try to help avoid crashes (e.g., blind-spot warning systems), we try to make roads safer, etc. Guns, no. Some people do vote for politicians who might push for laws limiting guns, but in office they don't do much because there just isn't enough broad political will to do so, because the voters really don't want to do anything about the issue because roughly half the population doesn't want any kind of new limits on gun ownership at all.

A major function of law enforcement is preventing murders (and to a lesser extent suicides), which includes those performed with a gun. That’s a lot of time and effort spent.

If by preventing you mean capturing killers after the fact and punishing them as a deterrent, yes.

Prison doesn't work as a deterrent for most crimes. It's useful to keep the honest population honest, and separate the dishonest one from the rest during a time.