overweight cat and skinny cat - how to feed?

Hi everyone, I'm new to the forums (hello!), and I am glad I stumbled upon you, because I could use some advice right now!

I have 2 cats, Aidan (male neutered, 5 yrs) and Mina (female spayed, 4 yrs). Mina is my plump girl. She was spayed at 6 months, and since then, has gained weight. At first, I thought it was only because of the spaying, but I've recently determined she likes to eat! She is on a plan to lose weight in a safe monitored way (Science Diet light, exercise, vet), but here is the problem I run across. The cats have previously been used to having a bowl with dry food down all day long - basically they could come and go as they pleased. They both shared one bowl, same food. While this worked fine for Aidan, who is at a perfect weight, Mina ate more than her share. So now, she gets a predetermined amount of Science Diet in her own individual bowl, while Aidan has his own bowl. She quickly figured out, though, that she could go to his bowl if she wants more. So I moved on to feeding their share in the morning, and putting the bowls away when I go to school. Problem is this - Aidan is now losing weight and he doesn't need to, and Mina has developed this annoying habit of taking the water bowl and dumping it all over the place (I assume she's annoyed that there isn't food a-plenty anymore), besides the fact that she also ruins their water supply and they both have no water in the day.

The suggestions I have recieved are to make a box with a hole in it so the skinny cat get in and eat and the larger one can't (the vet tech told me this). This didn't work well at all. Does anyone have any other suggestions? I want Mina to be at a healthy weight, but I also don't want Aidan to lose any more weight (he actually needs to gain a bit now).

Thank you so much! I will try anything...

I had this problem as well. What worked for me was to put skinny cat's food on top of the washing machine. The fat cat was too fat to jump that high, but the skinny cats could get to it whenver they wanted to eat.

You can try putting Aidan in a seperate room in the morning before you go and then in the evening when you get home. This way he can eat more of his own food. You can also give him some wet food in the evening to help keep the weight on.
With the water, I would get one of the bowls that comes in a stand. Weather it's plastic or stainless steel, they are a tip proof.

thank you both for your suggestions! I had just thought about wet food last night, and I am trying to figure out how high Mina can't go. Also the water bowl idea is great - I'll have to go check it out. Thanks!