Our Golden used to chase squirrels, birds, and rabbits. We let her do it in the back fenced yard, but tried to get her out of the 'chase' mode while out walking. She once scored a rabbit in her mouth
.
. My husband doesn't like squirells and rabbits in our back yard because they dig too many holes (and the rabbits actually ATE parts of our fence to get in and out)...so he was always happy to let her chase them.

I just saw a great episode of the "Dog Whisperer" where they trained the dog to stop going after other animals. It was quite simple...of course the guy is truly gifted. The worry is that they might take off after something and dart across the street, or I suppose pick up some nasty disease.

Cara