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I am sorry you are worried about Smokey. I am also sorry you have such an awful neighbor.
It is possible she put out antifreeze or mole poison but Smokey's symptoms could be caused by crystals in his urine. Kidney disease is common at his age. If that is the case, he will need a special diet. I recommend Royal canin renal food.
I would have him seen by a vet ASAP so he can be diagnosed and treated.
Please let me know what is found and how he is doing.