David has one dog, an old boy, but I have four Brittanys of varying ages and it doesn't stop foxes coming round and checking my place! I lost ducks and hens a couple of years ago from a paddock that my dogs regularly run free in.
We used to have 24 acres, hens, ducks, sheep, cattle - and a big German Wirehair as well as 6 Brittany's - she was sent out every night around 11.30pm, we used to watch her do a circuit of the fields, and next day we'd often see a fox strolling down through the fields. Hester would have killed any fox that came near and often came back with smaller vermin. They have no fear, not a bloody care in the world! I hate them.
So good on you for keeping them under controil