Here is my idea: One and done.
Everyone gets to own a gun until they commit ONE act of gun irresponsibility. After that they lose their guns forever. Get caught with em, five years in prison. Second time, 10 years. And so on.
Commit a gun crime? Done.
Leave your gun in reach of your toddler? Done
Operate your gun recklessly and someone gets hurt? Done
Use your gun while drunk or high? Done
I think our biggest mistake is treating people who act stupid with guns as people who merely have "accidents." There is no such thing as a "gun accident." There's only crime, stupidity, and operating your gun recklessly.