Unless you want to ban gun ownership outright, in a free society, there's always the chance a mentally unbalanced person might obtain a gun. My rejoinder to banning gun ownership is that if we're prepared to trade our freedom for temporary safety, no one is going to remain free.
"Show me just what Mohammed brought that was new, and there you will find things only evil and inhuman, such as his command to spread by the sword the faith he preached." -Manuel II Paleologus