There was a family of Canada geese in our backyard once before we got the fence. Jon had the great idea of sending [6-month old] Morgan out to chase them away. Apparently, Morgan had bounced halfway towards them when the two "parent" geese puffed up, spread out their wings, and started to slowly move towards him, of course, hissing the whole while.
Needless to say, Morgan was stopped dead in his tracks, retreated back to the safety of the porch, and Jon had to chase the geese out of the yard himself.