Personally, I think re-doing the cage with mesh cubes is the best long-term option. They prevent the cat from being able to reach into the cage even a little bit. I used them to make a rat cage and it keeps my one dog and three cats away with no problems. (Which is good, because my rats aren't scared of anything!)
Here's where I bought them online:
Mesh Cubes LD01-769 (Silver).
I hope that helps!