Big plate- Fill with water.
Smaller plate- empty and placed in the middle of the plate that is full of water.
Pot- set right on top of the dry plate.
Remove any possible bridges they might use, those being anything a branch that can fly by and set itself connecting over the water, it can be just a leaf, a plastic bag, anything, but as long as there is a section of water all around the pot, then they will just drown on the way to the pot.