Darwin rules my yard.
I don't poison snails often. That which does not kill my plants makes them stronger. Snails eat the weaker plants, and stronger ones that break their little snail teeth spread into the vacant area.
Evolution is interesting. Stepping on a garden snail results in a wet, final "crunch" that is probably the fourth grossest sound on Earth. Going to the tide pools by the ocean out here you find black sea snails that are the same size as the garden snails but have spent millions of years getting the crap pounded out of them by waves. You can stand on one of these buggers on one foot without busting them.
One of my many gardening rules of thumb: anything green that can be mowed flat and smooth is a "lawn."