Raccoons can climb but they can't jump all that well. Lock the cat door and tinker something together that provides a platform the cats can jump to so they can enter through a window. The raccoons will eventually learn how to rappelle down from the roof, but until that time you should be good to go.

A neighbor of mine who is well past the rappelle stage of raccoon training now has a cat entry that require the cats to jump up into a covered tunnel through which they then must crawl to get to the house. Apparently this combination has excluded all but the most intrepid raccoons for a period of several months.

Whether the cats can still get in, I really couldn't say, but my neighbors do seem to spend an awful lot of time walking to the door to facilitate feline entry and exit procedures...or, in the immortal words of Garrison Keiller:

"To all the cats I've known before
Who wanted to come in my door
And then they'd turn around
Ans wanted to go out
So they could come back in once more."

Cheers!
Claire