The ONLY thing that ever worked for me was netting the pond. Plastic decoys that look like herons didn't work, even though many will tell you they are solitary feeders. I have personally seen them in the wild, lined up on the banks during a baitfish run, just like human fishermen will do at the most popular locations.
Leaf netting will do, but it needs to be suspended at least 2 feet above the surface of the water. I have found that they will spear fish thru the netting, if their beaks can reach the water. They will often do this and kill fish much larger than they can eat. This is why I call them, "Birdzilla." So use the netting so they cannot duck their heads underneath it, while you are at it.
The good news is that they will eventually seek food that is easier to get and leave you alone for a while. But, keep a watch, as they will check back to see if things have changed again.
A small, yappy dog can work out, but at the risk of ticking off the neighborhood. My cats were no help in this regard, I think they admired the heron for it's fishing ablilities.