He drove the dog away.
Cacciare is also to hunt. So ,“Ha cacciato la volpe”, would be 'He hunted the fox". But cacciare il cane is to “drive away” or maybe “chase away” the dog. How would we know if the fox was hunted or chased away? ( I love foxes!)
It guess it should generally be obvious from the context. I suppose otherwise another word might be added to clarify (“cacciare via”, see the second definition on Treccani for the fox case, or “cacciare fuori” for different kinds of sentences), or another verb will likely be used to avoid any potential confusion. (yes! )