Cache'ing of web site

I maintain a small web site for a non-profit organization.  It's a very 
simple sight and works well.  My problem is that I don't know how to prevent 
it from being cached'.  I've inserted the following in the header, but it 
still caches and people who watch my site regularly don't see any updates 
until they delete their history.

<meta http-equiv= "Pragma" content= "no-cache">


Help!
Cindy

The site is www.camphopeforkids.org

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