We have a neighbor who pays to have the raccoons trapped and over the years the population has really gone down significantly. We had a sick raccoon in the yard last year. It turned out to have rabies which is a real problem in this area. Between the trapper and the diseases, we are finally winning the war.
I have a long, clay chimney flue pipe in the bottom of my pond. It is about 8" square and the fish can hide in it when the herons are hungry. Something like this:
http://superiorclay.com/firepl...
It was inexpensive and has worked very well. While it keeps the fish safe from the raccoons and herons it does not stop the snakes though. We lose most of ours to the snakes.
