How can I get my dogs to relax around other dogs?

I have three pit bulls. The youngest is about 6 months, the others a year and two years older, and they all came from a shelter. They get along fine with each other, but whenever we take them for walks, go to the vet, etc, they go crazy around other dogs. They whine, snarl, and pull on the leash so badly that we can't even introduce the dogs properly because we're afraid they'll attack them. I think the three of them rile each other up, too, but in some situations we just can't take them individually. What can I do?

You might not like this answer but you have a PACK and they are behaving as a PACK. Dangerous!http://tedthedogbooks.com