Place a heron decoy close to your pond. Herons are territorial and tend to respect the territory of others. Do not place a decoy up during March or April, when male herons are searching for mates, but keep it up from May through February.
Move your heron decoy regularly to ensure that the heron continues to think that it is a real bird.
Place an alligator decoy close to the edge of the pond. Alligators are a natural predator for herons, and the sight of one is enough to drive a heron away. Move the alligator decoy regularly to convince local herons of its reality.
Line the sides of your pond with loose gravel. Heron are used to walking on muddy stream beds, and the gravel is uncomfortable for them. This makes them less inclined to fish from the side of your pond.
Create a frame out of wooden stakes and throw a net cover over the top of your pond, securing it with industrial staples. The net should be at least a foot away from the surface of the water. This prevents the heron from approaching the pond. This can be a temporary measure, as herons do not return to a place where they were unable to fish before.