I am a firm believer in keeping all dogs on a leash.  My dog, Tucker, was the only dog I have ever had that I was confident to allow him off leash.  I learned this by walking on leash with him and he would always stay right next to me, no matter what.  Whether another dog would come up or a cat would run by, he would always stay right next to me.  So, I started taking him off leash for short periods to ensure that he would not wander and then we got to the point where I no longer needed a leash at all.  If he did start to trail off a little, I would call him and he would come right back to my side.  To this day, he is the only dog that I have ever had complete confidence in allowing off leash.  I am by no means advocating for allowing dogs to be off leash but based on Tucker’s specific personality type, I had no fear of him running off or hurting anyone.