There's only one type of successful gun free zone, on an airplane. It has been highly successful because the strict security check before one can board an airplane. (Before you use 911 as a counter-argument, please know that the 911 terrorists used a box cutter, which was legal to bring on a plane at the time). We have gone many years without any firearm related crime on an airplane, even though hundreds of millions of people travel by airplane every year.
Therefore, we propose that a "gun free zone" can not be legally declared/created without airport level security implemented. A "gun free zone" without the proper security check, is simply a sign that says "unarmed people inside".