Try Rocks in your plants!

To keep Kitty from digging in your house plants, purchase inexpensive river stones or collect attractive stones and cover the dirt in the top of the planter. The rocks won´t hurt the plant, and will allow water and fertilzer through to the soil.
Guru´s Note: I would suggest you use stones/rocks no smaller than a golf ball, or Kitty could have just as much fun digging up small stones as he does the plant.