NormK, Are you sure they not related to the Chinese? I was once told that China could start marching their people in the ocean and before they got in, it would flood the world.
It is a war you not going to win very easily. Here my possum problem only has lows not complete win of the war just a just a few battles. They are back again after raising a new crop of warriors. Two already got killed (by car) and I have lost at least one hen as she stay out with her young. It was the first night she stayed out and I now raising the orphans.
You just got to have patience and know you are not going win completely. If you get to a stand-off level you are doing good.
Now for removing every plant you could like fellow I here of from New York state where he did his whole yard in dyed green concrete. He was tired of cutting grass and the city's harassment everytime his yard got a couple inches taller than the neighbors lawns.
