If a person cannot secure their weapon, there should be no 2nd Amendment protection. There is no need to deny responsible gun owners their 2nd Amendment right, but those rights have inherent responsibilities.
If a firearm is used in any crime, the owner of that firearm is to be held responsible in that crime to at least negligence. This liability should also be extended to firearm retailers. If a citizen cannot show proof of a means of securing certain types of weapons, selling that weapon should be a crime of at least negligence.