Dear tm1gate - You can file a suit for slander against your neighbor assuming you have an independent witness who would testify that these statements were made by the neighbor. I would assume you can also prove the fact that your cameras are not directed at their outdoor shower.
You can sue for damages however the mere fact of a lawsuit sometimes will stop people from continuing making these statements. There are no criminal charges you could file against them so a civil suit is your only option.
I am not permitted to actually represent clients from this website. I don't think you need to explain slander to anyone since it is simply the communication of lies and falsehoods which cause damage to another. You can write a letter simply stating that if the activity does not stop you intend to seek legal action against them for slander.
If they do not stop then you can contact a local lawyer and file a suit. It sounds like these people are not going to listen to a letter if they are prone to lie in the first place but you might as well try.
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