Registration of every weapon and background checks on all sales. Weapon must be registered with new owner before acquiring the weapon. Stiff penalties if a weapon is used to commit a crime to the person it belongs to (if you sell under-the-table to a person who commits a crime or don’t properly secure your weapons and they’re used in a crime.) Would put the kibosh on many straw purchases and force people to properly secure their arsenals in safes etc.
Picked close the gun-show loophole above.