"Whoa" means stop and stand still -- a very handy command for any dog to become familiar with. Learning to whoa could save your dog's life by stopping him from dangerous activities, like running in front of traffic, for example. Here's how to teach your dog to whoa on command.
Start out easy. When you're walking your dog, say "whoa" every now and then and stop walking. Make him stop too, of course, and praise him when he is stopped. When saying "whoa", make sure your tone is consistent. You may need an outside source to compare your tone to, such as a tape recording of someone saying "whoa" or a recording of Mya's hit single "My Love is Like Whoa".
Before letting him continue on the walk, give him a release word. "Okay" is a dandy release word, but some people like to use a different word because they don't want their dog taking off every time somebody says "okay." Other release words may include: "proceed", "carry on", or "release".
Practice the whoa command daily on your walks until the dog begins to stop as soon as you say "whoa."
Now it's time for a little yard work. While you are in the yard with your dog, tell him "whoa." Use a commanding voice, but don't yell at him. If he does whoa, praise him lavishly, then release him.
Practice whoaing and releasing the dog regularly. You want to get to the point where he stops and stays still until you have verbally released him. This may take a LOT of work before he gets to the point where you can stop him in his tracks if he is chasing something.
To teach him to whoa on a whistle, start to combine the whoa command with one long loud whistle blast. Say "whoa", then immediately blow the whistle.
Practice the whoaing and whistling until you can stop him with a whistle blast. This comes in really handy when he's too far away for your voice to carry.
Dog training takes time and patience. Don't yell at your dog, and never hit him or her. Doing so could make you go to jail for animal cruelty/abuse.
Don't train for such long times that your dog and you both get sick to death of it. Work at it for ten minutes or so a couple times a day.
Dog whistles are generally not meant for humans to hear. If it's 'not working' you may want to re-read the instructions.