lucy24 - 9:41 pm on Oct 26, 2012 (gmt 0)

however if added to a URL they may still resolve the page

That is the default behavior for static extensions such as html. If it's a major problem, and you use no parameters at all, you can put the line
AcceptPathInfo Off
in your htaccess. But it's rarely worth the trouble, and you may accidentally switch off hidden functions such as analytics or auto-indexing.