What ever you try, it won't work 100% unless you use chemicals. I find it's impossible to totally stop them, and i personally am against using strong chemicals in the garden.
Natural ways are copper mesh / preventives or traps, to trap them then move them. My friend uses a type of slug preventing gravel in his greenhouse, and that works real well.
Despite being a virtually organic gardener I do use slug pellets to start with. After any rain when they certainly emerge in droves I go out with secateurs and snip them in half. No I'm definitely not a Buddhist when it comes to slugs versus my veg!