How can we ensure our Hotel in Beijing will secure us a taxi from outside on our departure date.

We will be staying at The Sheraton Dongcheng District when we visit but lots of comments from guests appear complain around trying to get a Taxi outside this Hotel and how notoriously difficult it can be due to the confusion by Taxi drivers as to where the actual collection/entrance is. One man complained that he had to wait 1hr and 40mins outside of the Hotel for Taxi he had asked the conceirge to book for him and consequently nearly missed his flight home. Any practical suggestions on how we might avoid this happening to us? Your help is most appreciated.