Without seeing the spot and knowing HOW wet it is I don't know if my suggestion will help, but the very first thought that comes to mind is to plant something there that drinks large, large amounts of water. It will do two things: one is take away much of the water and stabilize the soil and the second is put something in your wealth area that represents and in fact is growth that should translate to growth in your wealth.
Also, an avid gardener let me suggest river birch trees. You would have to go to your nursery to inquire about the exact variety of river birches that will sop up a lot of water. Also, NON-invasive bamboo. If you buy the invasive kind you will have other problems later, but the non invasive kind drink a lot of water and are very fast growing. They are also very auspicious in Feng Shui.
Most important of all is that you must not allow your neighbors' acts let a pervasive attitude of negativity befall you. Try to stay positive as you do your cures. You may even end up with a better situation had this never happened!
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