They don't have to be roaming free to do harm. There was a case last year I believe about one that tore down a fence and killed a child in the back yard next door. An 80 lb dog with blood in it's eyes can get through a very strong fence.
Well clearly you have to provide more than adequate containment for the dog being contained. I have two escape artists among my four dogs and I have had to go above and beyond the normal fence as a result. It is all about effort and responsibility. If someone is not willing to accept the responsability then they shouldn't be a dog owner.
