Pass a law that the ownership of military/assault/combat personnel weapons requires membership in a well regulated militia.
The militias should; be of a certain minimum and maximum size; should not be allowed to coordinate, gather, or communicate with other militias; should have prudent procedures to secure weapons in an armory (the location of which does not need to be revealed to government); must maintain accurate membership roles and weapon/ammunition inventory; must have prudent measures in place to insure that weapons cannot be individually accessed by non-members and/or members in states of emotional distress or with signs or histories of mental illness.
Any breach of prudent controls may result in restrictions of all individual members future gun rights.