This may not be the exact solution you're looking for, but if you buy a water unit that's heavier, Leo won't be able to push it around. I read somewhere that cats like to see moving water, so maybe you might consider getting a cat fountain?

I bought the drinkwell fountain for my cats (I have 3!), and they love it. The base is huge, so the unit shouldn't be able to be tipped over. The things to be aware of if you go through with buying this is that it's a little inconvenient to clean (since it's so big) and the water container doesn't have a flat top (meaning you have to stand there and fill up the container every time instead of being able to walk away and do something else for 30 seconds).