I'm getting slugs in my shower, and I mean lots of them, how do I get rid of them?

Every night I will find 6-8 slugs in my stand up shower and I can't figure out how they are getting in there. I clean the shower every other day, and now I noticing that they moving out to the bathroom floor and other areas of the bathroom. I put salt on them pick them up with a toilet paper and flush them, but everyday they come back. I need help!!! What can I do?