what will keep a hawk out of a yard?

Ravens will discourage hawks from hanging around a specific area, because ravens, being territorial, will attack them. Sure, the hawk is much more powerful than a raven with its sharp beak, streamlined wing feathers and razor talons, but ravens work in teams, while hawks do not - so the hawk is easily outnumbered.

Some species of aggressive owls can also do the same job as ravens. Owls too have a sharp beak and razor talons, like the hawk, and they also have feathers designed to make them silent in flight enabling them to sneak up on other creatures, but they usually only bother moving at night. The Great Horned Owl is a well known hawk predator, they will approach the hawk from behind or above, using their silent flight skills, then swoop down, clutch the hawk in its razor talons and either bash the hawk's skull with its beak or rip into the hawks throat with the sharp tip of their beak. Anything that attempts to escape from the talons of an owl will just be shredded by the razor talons. Not a lot of people realise how fierce a hunter the owl actually is.

If you don't wish to cause distress to the hawk or would rather not be swamped by ravens or owls, you could invest in an electric owl lamp. These are owls that light up so they can be seen from the sky, acting as a sort of scarecrow.

Only problem is that once the hawks test the owl and realise it's fake, they'll begin ignoring it, again just like an ordinary scarecrow.

If you are trying to protect animals in your yard from hawks, you can use anti-bird netting. This will prevent the hawks from landing and will protect the animals in the yard enclosure.

A trained guard dog will also work. It's best to invest in a dog that was actually bred for hunting birds, since it is already in their genetics to seek them out. Such as German Shorthaired Pointers, Brittany Pointers, English Pointers and Golden Retrievers.

Make sure bird feeders are under a canopy or somewhere out of direct "bird view" sight. Smaller birds who the feeders are intended for will still spot the feeders and tell their mates where they are, but a predatory bird like a hawk will miss them. If there are less visible prey in your yard then hawks won't bother coming by.

In many places it is illegal to shoot the hawk or set up traps for it, because they may be a protected species. However, a person cannot be blamed for the actions of another animal against a hawk as long as the person didn't actively encourage the animal to go for the hawk.