A heron decoy placed by the pond during March and April can actually draw a male in search of a mate.
It is best to wait until late May to put the decoy out.
The decoy is a very effective method in June through February because once he picks his mate the heron then defends his territory.
Herons stay out of other herons' defended territories when not in search of a mate.
Remember when you use a decoy to periodically move it around to keep up the appearance of a live bird.