Unfortunately you have no legal recourse against your neighbor if his cypress trees that he planted on his property have roots that travel onto your property causing a problem with your septic field. There is a lot of law on the subject that you have written about throughout all states in this country. The rationale for no liablity is that the conduct of the tree's roots that may or may not impact a septic system is not negligence by the person who planted the trees or owned the land where the trees are situated.What you should do is place root preventer in your septic system to prevent roots from growing into the perforated leach lines on a routine basis.