Leash Law

People who let their aggressive dogs run lose without leashes to go after my dog (or a client's dog) tend to piss me off. They claim the dog is under their voice control, but this is rarely the case. Take tonight as an example.
I was walking a client's dog - an 11-year old black lab named Sam - back to my house, after I'd walked him down to his house to pick up the client's mail. I noticed another dog at the other end of the block, but I keep walking towards them, thinking the dog is on a leash. Suddenly, I realize the other dog isn't when the owner starts calling it. WTF? This is a city street. That dog needs to be on a leash. Judging by the slightly frantic tone of the owner, I deduce correctly that the dog may be hostile. The other dog runs towards Sam and I, growling as it comes. I do the appropriate things: I put my foot - well protected by a boot - in the dog's way, while simultaneously yelling at the dog to "back off, you little shithead!"
Fortunately, the dog only gave Sam a few seconds of sniffing before it continued on. I was mad, though. Dogs that can be aggressive to people or other dogs need to be on a leash, no exceptions. I told this to the owner, yelling at him "if your dog is aggressive towards other dogs, put it on a damn leash!"
Of course, the owner didn't, just continuing on as if nothing had happened. As I continued, I heard the owner say something about "please don''t kick my dog.." but I didn't catch all of it. I didn't kick his dog; I only put my foot in it's way so it wouldn't get too close to Sam, as I didn't know if the dog's intentions were hostile or not.
Let me make one thing perfectly clear: if a dog I own, or a dog I am taking care of, comes under attack or threat of attack from another dog, especially another dog that is illegally off leash, I will do whatever is necessary to protect the other dog and myself. If this includes inflicting injury or death to the other dog, then so be it. I won't like doing it, but I believe myself capable of doing such a thing under extreme circumstances.
I guess there is a point to this post. Seattle Municipal Code (SMC) 9.25.084 says that it is unlawful for an owner to permit any animal when unprovoked on public or private property to "Chase or approach a human, on property other than that of the animal's owner, in a menacing fashion or apparent attitude of attack, which may include but is not limited to any one or more of the following behaviors: snarling, baring teeth, growling, snapping, pouncing, lunging, attacking, or attempting to bite."
The dog that went at Sam and I was growling and baring its teeth, and neither one of us provoked it. So, moral of the story:

Keep your dog on a leash!