Slug and Snail Trap

This year in spring I found slugs everywhere. So I have declared war to them.
This trap includes a watering system. Slugs like to have cold and humid. The green roof has a water basin in the middle to cool in sunshine. Both roofs have water channels down to bottom. Make a groove in the ground, it will be humid there. Slugs will sleep there over the sunny day and you can find them. This groove has to be humid but not a lake, slugs are afraid from water because they cannot swim. This model files contains a cuboid. Don't print this. It should be a piece of glass or any other 'cold' material. Put some salad onto and the slugs will love you (at their last day). Check it daily and water it.
Slugs like: rhubarb leaves in the early spring, red poppy leaves and the hairy cover, salad, tagetes flowers.
It would be good to scale it by 2. I have not done because it takes so much filament :-(

How to kill slugs? I put them in a plastic mug and then I freeze in the freezer (My wife hasn't found it yet). Then I put it to compost.