[pmwiki-users] prevent users from changing seachbox parameters

[JB]

I put (:searchbox group=Main size=25 label=Go:) into
Site.PageActions.  I do a search.  The url for the browser
has the search information in it.  If I remove "&group=Main"
from the url in the browser it will search all the pages.

I know I cannot stop users from manipulating the url in
their browser, but how could I prevent that url from
changing the search to be different than specified in
the searchbox?