I totally agree that dogs should be under control, and in the street any responsible owner will keep their dog on a lead. The problem is that in a park, when off the lead, a dog can suddenly run off, if the temptation is strong enough (e.g. food - see my previous post), or if it is being chased or has been frightened by something. These things do happen, and while there are some dogs who have perfect recall, and will always come back on command in any situation, there are some who - occasionally - just will not. In a situation like this, a dog can suddenly run away from the middle of the park, where it had been playing safely, and out of an open gate into the road. I have seen it happen on more than one occasion. Dogs can run very fast, and there are times when an owner can do nothing to stop it. It is these situations where keeping the gate closed would minimise the risk to others - drivers, cyclists and pedestrians.