I think Colorado has enough problems, what with terrorists and such, they should just start impounding their citizens instead of the dogs. And, just for the record, ANY dog can be made into a mankiller. ANY dog. If golden retrievers were as muscular as pits/staffordshire types, you better believe that the people who breed/train them for fighting/attacking would be using golden retrievers.
And if they have such a problem w/dog fighting/attacks, I think that reflects more on the citizens than the dogs.
All in all, Denver is using a very wrong-headed, ill-thought out plan. And like the guy said, no proof that it works at all.
BTW, I don't like dogfighting, it's so hard to get boxing gloves on a dog...