Best way to get revised content vsited by search engines

What to do when content is significantly revised or updated

[aijohn]

I am significantly adding to the information on some pages and in the process probably changing the emphasis on certain keywords.

These pages were indexed by the search engines when the content was not as developed. What's the best way to get the new content to show in searches? So far, I am including a last revised in the meta tags. Is there a better way?

[Gargen]

best way is sitemaps, i started to get 50k google hits in a little over a day so i actually took them off for a while

[aijohn]

Did some more research and decided my LastModified wasn't doing anything as the pages are dynamic.

Found this (for php)

header("Last-Modified: " . gmdate("D, d M Y H:i:s", getlastmod()) . " GMT");