I had this problem with my Sasha when she was younger, and I put foil around the plant pot so that she couldn't get to the dirt. When she realized she could move the foil and still get to the dirt, I had to wrap the foil tighter. She soon learned and/or outgrew it! You just have to be patient.

The idea of water flicking at the cat is great! It worked for my older cat, Tabitha, when she was younger. However, Sasha LOVED it.... and would look at me after a water squirt as if she wanted more! These kitties.... all are different!

Good luck!