Shopping Carts and Sessions

Hi, I have been playing around trying to build a 'perfect' shopping cart. A brief as possible feature list: database driven, fully indexable by search engines, and can operate without cookies. I decided to use Apache's mod_rewrite to change a standard looking URL into something php can use easily. ex: http://www.mydomain.com/produce/carrots/spec1/94d0bb50cd.html would become http://www.mydomain.com/index.php?dept=produce&product=carrots& specials=spec1&PHPSESSID=94d0bb50cd Now for the problem, when a search engine spiders this it will be including the session id. Unless I do some kind of checking, I could end up with multiple users having the same session id -- if they click into the site from a search engine or a bookmark. The best solution I have come up with is to add a timestamp variable inside the URL. If the timestamp is more than 1 hour old -- reassign a new timestamp and session id then build the page as specified by the other variables passed to the script. I was wondering if anyone knows of a more elegant solution for this problem. thanks, don