It seems that if cats aren't trying to consume your house plants, they're doing something much worse to it. That "something" is bad for the plant, bad for you and bad for the cat when you catch it. If for some reason your feline companion has decided that your household plants are an alternative to the litter box, it will take a bit of convincing to get him to see it your way.
Make the plant smell completely unappealing to your cat. Spray Bitter Apple on the leaves or place citrus peels in the soil to keep kitty out.
Cover the soil with aluminum foil, crushed eggshells or rose bush clippings. If the soil doesn't feel good on their paws, they won't be as inclined to dig in it.
Move the plant to a place that's hard to get to for your cat, such as up on a high, inaccessible shelf or behind a closed door.
Keep a spray bottle handy and give your cat a shot of water every time you catch him digging in the plant. Over time, he will begin to associate getting into your plant with getting wet.
Cover the plant with netting so there is no way for kitty to access the planter and do terrible things in the soil.