london: To 404 or 301... that is the question (Search Engine Optimization (SEO))

Hi,

I am trying to decide whether a 404 or 301 HTTP header would be more appropriate in my scenario. On a practical point, a 404 ior 410 seems the most logical thing to return in the human sense, but I'm worried about what search engines might think...

I have a site where teaching jobs can be posted for free. URLs are like /job/1 /job2 etc. Each one is on there for about 2 weeks or so, but some can be on there for a good few months. Whe