charlie emergency!!

My little Charlie was really sick yesterday, meowing a lot and lacting like his bottom was really sore. I looked closer and found blood. I took him to the vet and they told me that his urethra was completely blocked. They had to give him a catherter. They said he would have died if I hadn't brought him in. I went and got him some urinary health food last night, but I really don't know what else to do to prevent this. He is only a year and a half old, but he is pretty overweight. The problem is, I also have another cat who is 4, but he is not at all overweight. They are the kind of cats that go back and eat their food several times a day, not all at once, so feeding them seperately is not a good option. Help!

Build a box with an entrance that only your skinny cat can fit through and put his food in there. That way Charlie can't get to it and has to eat what is out side (diet food). Good luck!