Out of curiosity, what is the type of environment are we talking about here?
I am not aware of any ruggedized versions of the 8851 out there... You can get all sorts of wall boxes and containers for them but the phones themselves are not ruggedized.
The closest thing I can think of are the silicone cases you can get for the 8851, but those are mainly meant for healthcare so the phones can be wiped down with harsh cleaners.
There is the Cisco 8821/8821-EX ruggedized option but that is a wireless handheld type. If you need a ruggedized desk-phone, you may have to look at 3rd party.
