I agree with Arlene about the beer. Or you can also sprinkle table salt all around the plant. It gets on the slugs and dries them out.
You can also spray a mixture of hot sauce and water onto the basil, just make sure you wash it before you use it and you have to do it after every rain.

Another easy thing to do is to cover the basil with a net.

This advice is coming from the black thumb of gardening but I do do well with herbs and also shade loving plants :)

Karen

Live long and prosper