Snail barrier for plants

I like to do some guerilla weed farming in random fields. The biggest problem are the snails eating your plants. 

I tried everything, and came up this idea. Take a piece of PVC pipe 40mm and cut it to length. I used my saw to cut some holes in the bottom part for roots to grow out off.

Put some tissue paper in the bottem part of the pipe, cover it with aluminium foil and fill it with soil. I left 8 cm free from the top. 

Grow the plant under some light tills it's big enough to go outside. Now remove any plants around the spot and remove the tissue paper, put the pipe 1/3th in the ground. 

Put a mixture of petroleum jelly and salt on the bottom of the umbrella and slide it over the pvc pipe. Any snail or slug wont be crossing over to your plant anymore.