Patrol your pond on a regular basis. Herons are shy birds that prefer to hunt unnoticed. If you make it a regular practice to scare herons away from your pond, they may eventually look for a quieter body of water to frequent.
Add rock features, such as underwater ledges, or vegetation, such as water lilies, that your fish can hide under. Add spots in your pond that are at least 3 feet deep, as herons cannot fish in water that deep. If a heron cannot find food, it will look for other bodies of water in which to fish.
Place a net over your pond. If you have a relatively small ornamental pond, you may be able to cover it entirely with a protective netting.
Set a motion-activated sprinkler or two that will blast the bird with water as it approaches your pond. Motion-activated devices that make sounds can also be used to scare away herons.
Place a heron decoy or fake heron in or near your pond. Herons tend to be territorial and will usually not fish where another heron is present.
Add a floating fake alligator to your pond, which may also scare away a heron.
Plant high brush or bushes around your pond. Herons prefer to hunt where they have a clear view of any predators that may be approaching.