A number of entries here on keeping chickens, but not much on other types of fowl. I don't think there's much of anything on geese. So from Mother Earth News:
Watch-Geese: The Natural Farm Guardians
Utilize the unique characteristics of geese to make them natural guardians and perfect protectors for your farm and flock.
The article talks at great length about how vigilant they are in the daytime, and if goslings are raised with flocks of smaller fowl--chickens, quail, etc.--they will defend their surrogate families from predators. And the article starts with a tale about how the sacred geese at the Temple of Juno alerted Rome to the invasion of a group of Gauls while the dogs did not. Then it admits that geese don't see well at night and are vulnerable to predators...
OK! And it says nothing about ganders... Which is interesting. In one of the BBC farm series--probably the Edwardian Farm--a fox got into the goose shed and nearly killed one of the geese. So they got a gander--which was an aggressive, domineering bird--and set it among the geese. End of fox problem, but a real nuisance for our farmers.
So, there is obviously more to raising geese than the article suggests... But it's still interesting.