Questions about how the government can solve this are misplaced.

There are already laws to protect against school shootings. For example it is illegal to possess a firearm on school property and it is also illegal to murder people. People who don't obey the laws are criminals -- would another law prevent criminals from engaging in criminal action? Can we really be free and safe through the restriction of personal liberty by the ones with the most guns (government)? What is the incentive for a police force, who profits from crime (more crime = more laws = more police), to prevent crime? What are the options for a tax-burdened citizenry to choose a safer school environment?

So many good questions we should be asking, which do not involve government restricting liberty.