Treez....your probably talking about a certain "strain"

of bulldog I would imagine.
I've had APBT's and American Bulldogs and crosses of the two for years that I have kenneled and never had any issues concerning fence fighting/ aggression or breaking of teeth.
As you say....just different kinds of dogs.
Again...I don't have an issue with anyone using chains....I just think pens are better and I myself chose not to use chains.