My turkey does a great job keeping the chickens alerted, but my ducks have always hung out by themselves. I'm hoping the geese will be more likely to hang out in the same spot as the ducks, and keep an eye on them. They also have a lot of trees for cover in their yard I was planning on cutting way back for more sun, but maybe I'll leave them.
Or cover their whole yard in deer netting. It might not stop a hawk, but maybe slow it down enough to let everyone get to cover. The ducks aren't allowed out of their yard during the summer unless someone is there to supervise anyway, since they like to go poop in the kids wading pools.