Annnnd those wild birds have a whole lot more space to get away from each other than birds that are penned together. In my experience, even one goose, no matter how well they get along with the other poultry  can do some serious damage to a full grown duck if it feels so inclined. Why would you want to put your tiny calls in a situation that will very likely end with them being injured or killed by birds much larger, and much more territorial than they are? If you want geese as flock protectors, give them their own digs with no one else encroaching on their space, at the very least for bed time accommodations. Lots of people free range everyone together but house them separately. Then at least if there is an issue between groups nobody winds up dead in the morning.