Rather than trying to find plants that will survive slugs/snails why not deter them and the best way with tubs and planters is to use copper tape that you can buy from most garden suppliers.

tried that and also copper wires around the tubs, but thanks anyway.

I use begonias in some tubs the slug and snails don't touch them, but they love petunias.

Slugs and snails don't like plants with very fine hairy leaves, so anything that fits that description, Derek.

I found this blog post interesting about plants which seem to survive slugs and snails:
http://www.growsonyou.com/taz/blog/23595-slug-free-plants

Maybe it could give you some ideas?