Ah yes, the armadillo-like arthropod / isopod. I have them too. I have tons of them in the rocks near my deck. I get about 10-20 a day that think they want to take a swim.

I know some pesticides are labeled to kill them. If you search some of the organic gardening web sites you might find some other ways to control them. I can't speak for any of the methods because I don't worry about them, I just vacuum or skim them out.