I'll go one step further than the OP. First, every gun must be registered. Any gun used in a shooting by someone else other than the owner will result in the owner being as guilty as the shooter. This would not be the case if the gun was stolen. A gun taken by a family member is not stolen, it is taken without permission. If a person is not willing to accept that responsibility they should reconsider buying a gun. Drastic as it may seem there would save lives.
Individual states have attempted mandatory registration requirements, only to be met by widespread opposition from the public. When the public refused to comply, the individual state governments realized there was nothing they could do without public cooperation, and did not pursue other avenues of enforcement.
Locking devices only work once the firearm is unloaded, and thus unable to actually be discharged to begin with.