we have a fake owl actually too. our run is covered in chicken wire....
but I did say in a different thread.... I don't know if and what it's supposed to scare exactly BUT knock on wood, we haven't had any hawks or owls......
Well, as far as the owl... we have not had a problem with any predators at all so far. We put a solar light in it so that at night its eyes glow red and it looks lifelike. So far it has worked for us.