I'm so sorry. I know EXACTLY what you're feeling. I know EXACTLY how impossible it is to keep one cat away from the others food. I solved it by simply puttig all 5 cats on the special food that Pouncer needs. It was the only way that worked. Pouncer REFUSED to eat his special food when I locked him in the room by himself. They refused to eat thinking Pouncer got better food than they did. So I'd open the door and Pouncer would fly out to eat what the other guys had and they'd fly into the room to eat what Pouncer had. It just was not working.

Now we have a nice little scheme going. He gets his special food at night as a treat. This food actually dissolves the crystals. He gets the Eukanuba Low pH diet (the crystal reduction food) at night as a treat and then I feed him and everyone else HIlls WD (which is a prescription weight management food, but perfectly safe for a cat susceptable to crystals). I spend $40 a month in food but its weel worth it because I have not had a recurrance of Pouncer's crystals in a few months. When I consider the vet expenses & all the cleaning product expense related to the crystals... I'm quite happy to spend the extra money each month on food. I figure it sounds more but is actually less since I'm not buying meds, paying for urine tests, buying enzyme cleaners, washing and rewashing a hundred things, etc.