This blog post from ParentingIdeas.org lists how to set up the major search engines to default to safe search mode. None of these will be 100%, but they do filter out most of the inappropriate search results. For market leader Google, it’s very simple.
1. Go to Google preferences.
2. Select safe search and click save.
That’s it. Google with set a text cookie in your browser that activate safe search every time you visit Google. Do this from each computer in the house and you search results will be relatively protected. The cookie is browser specific so you’ll need to do it with IE / AOL / Firefox etc if you use multiple browsers.