Cats are often fascinated with pots of soil - to them, it's like another litterbox! Covering the soil with tinfoil (especially if you scrunch it up a bit) might work better than newspaper - cats generally don't like working on scrunched up foil, both from the feel of it and the sound it makes.
You could try scattering orange/citrus peel in the pot too - most cats can't stand the smell of citrus, so that might be enough to keep him away.
If all else fails, there's always the option of a motion activated air spray, such as PetSafe Ssscat spray
. It will give out a harmless but annoying burst of air when your boy goes near the plant pot. I would definitely try the other options first though.
Whilst this training is going on, it might be worth spreading newspaper or something around the base of the pot - just to make cleanup easier if he doesn't get the message straightaway.
Hope some of these help