Attack of the slugs!

Every night I do battle. I attempt to feed my cats without the slugs getting their food. We have done salt rings around the dish, but they are "smart". They talk our cat into sliding the dish outside of the ring or close to the house where they try and stretch over the chasm to get food. Occasionally, there is one who didn't quite make it and ends up in puddle in the salt... which simply dissolves the salt and slowly opens the ring up to the other slugs. Gross and frustrating! I need to build a specialty dish. I am thinking of gluing a dish to plywood and gluing salt all around it. I wonder if salty glue would stop them....