Dont kill a heron, their such beutiful birds, If a saw a easy snack, I would try to get it. Get a dog, and post its area around you pond. That will end the blue herons reign.
I too have lost fish to a heron this month its all netted and attached to post and fencing I have plastic herons decoys of all sort I don't know how it does it , or what else to do this is part of my pond it has solar lights round it come on when dark