chachi,
You always give good advice, I look forward to reading anything you say.
In ALL cases, one should make sure that the area which they go into is secure, maybe with...
High Fence,
Locked Gates,
Adequate protective Canopy, for protection from flying predators,
Thorough check of Bottom of Fence for possible exits,
Cover from Sun/Rain if they're stubborn and want to stay outside,
Water,
Elevated (dry/cool) place to lay/sit,
Adequate window(s) for observation of their activities.
I have all these things in place, and I'm sure I forgot something. But when one is careful, I think a Doggy Door is not as risky as one would think, and in my case, EXTREMELY handy, because of their MANY trips to the Potty, and frequency of the Zoomies.
Additionally, in my case, both mine are highly territorial when here at the house, and they'd raise all kinds of h*ll, if someone approached for any reason (friend or foe).