If you have an 20-year-old unstable nutjob for a son, either don’t purchase deadly weapons, or keep them damn sure where he can’t get to them.
If you look around the US....there’s probably 100k homes where some nutjob is in the house, and there are guns in the house. Unless you made up a rule where guns had to be stored in a special gun locker with a unique single key...that’s about the only safe way to allow the weapon to stay under such a roof. Course, the nutjob could easily break into the neighbor’s house....steal his one single rifle, and shoot a dozen people with it.