HOW DO I DETER HERONS FROM STEALING MY FISH?

I have the same problem! I even live in a very urban area. The only think I know of is that they sell a fine black netting that is placed just above water level of the pond. Only problem is that if you have water plants that grow up out of the water. Then you have to cut the netting to fit around them. About the urine thing...my dogs pee in the pond all the time, and the heron/egrets still eat my prized goldfish.