I have been looking for a sliding glass doggy door system for a bit too, without much luck.
In our situation, it'd be in our sunroom where we'd use it - it'd be supervised (We can close off the sunroom so they won't have unsupervised access)...just save me the trip of walking on the freezing cold floor to open the door/close the door. We have a large picture window that I can see the entire yard, and they are not left out unsupervised. As the PP suggested, you should not leave your dogs outside unsupervised - even in your fenced in yard.
Please update if you find anything!