A friend of mine got a pond with fishes in his garden, that longed acted (unfortunately for the fishes) as a food store for herons migrating. He then used a fake heron that worked pretty well the first year, but not the second. Next years he moved the plastic heron every couple weeks during the period he knows they comes and apparently this works.

He’s from Europe and use his own experience but apparently this site may help for US residents

https://explorer.audubon.org/explore/species/1387/great-blue...