Text editors

I am having some difficulty trying to work around an odd behavior whereby my divide-by symbol (÷) doesn't properly display.  My preferred work-around is to type in the following in raw HTML: ÷

This will allow proper display under both utf-8 as well as iso-1859-1.  Unfortunately, if I go back into the editor later I find the editor has replaced these characters with the symbol itself.  This, then, will not display properly under utf-8.

How can I prevent the editor from re-writing my text?