No one really regulates the leash law around here. Many dogs are let off lead, while some owners are smart enough to know that their dog is not well-behaved enough to be set free. Unfortunately, I've only met three dogs off lead that have done well- a Black Lab, a German Short Haired Pointer, and an Old English Bulldogge. I've had bad encounters with two Black Labs, some sort of huge white mixed dog, and a Finnish Lapphund, all of which attacked my AmStaff/Whippet mix and broke skin while we were on walks. One of the Black Labs had an owner chasing after it, and the huge white thing had broken it's chain.
I think that people need to keep their dogs on leash unless they know for sure without a doubt that the dog will come back on first recall. Because of the people who had not trained their dogs to come back, I now have a dog who's terrified and reactive to big dogs. Every time she was attacked, I had to carry Rock above my head and run away as fast as I could from the attacking dogs.
Basically, if you aren't 10009% sure that your dog will listen to your recall, then keep it on a leash at all times. Just because I have a "pit mix" does not mean that because your huge furry dog that my dog stands no chance to winning against comes up and sinks it's jaws into her skinny Whippet body, that does not mean I'm in more trouble for a dog fight. Yes, Rock will fight back- it's in her nature. But, at least my dog is ON A LEASH and I can PULL HER OUT OF A FIGHT. I have carried my dog away as she's bleeding on my shirt because of some idiot's uncontrolled dog.
(this is turning into kind of a rant, isn't it?) That said, if you do have control of your dog and your dog is not reactive towards other people, dogs, wild animals, etc, then feel free to let it off leash and go play fetch in the park. That is fine with me. I know I can't let Rock off lead because she's become so reactive to big dogs (and pretty much everyone around me has a big dog) and also because she is mostly Whippet and will be gone before even a race horse can catch up to her.
What I'm saying is (and I am saying a lot... sorry) you need to be responsible.