In my opinion the Automatic Pool Cover is the best safety device you could ever purchase for your pool. As long as your pool is covered, no one can gain access to your pool. The same cannot be said for fences. Any motivated child or teen can easily scale a fence and be in an unsupervised pool in seconds. As a parent of 3 little ones this is a scary thought.
That being said I am also a proponent of multiple layers of protection. I think a fence and a safety cover combined are great barriers to reduce the chances of a water related accident.
More and more municipalities are getting on board with allowing a pool to go unfenced as long as you have an automatic pool cover. The best way to find out is to make a quick phone call to your local building inspector to find out for sure.