Hi,

1. You can use some Velcro or double-sided tape to secure the flap, so it requires more of an effort to get it open. All but the smallest dogs should have no problem, but the cat might give up if it's too much work. Close off the room that has the doggie door.

2. Petsafe smart feed automatic dog and cat feeder

3. Check the Wyze Cam Pan

On the market there are myriad of tools that can help to watch over your pet. Small cameras, GPS trackers and sensory devices are widely available online or in pet stores. Personally, my cat has a small GPS tracker named Paw track introduced into her belt. In this way, I know all her movements and trips outside the house. Also, since she started to have hiccups, which cause suffocation I decided to put a sensory detect on the door. You know, when these hiccups start she rushes outside to get more fresh air and smooth them down.

We have installed a controlled access for our cats and it works perfectly. I can absolutely recommend such a device, it provides much more relaxation - for the animals and for you.
We have used this one and had good experiences with it:
https://www.amazon.com/SureFlap-Microchip-Cat-Door-White/dp/B003EGIM3O

The Buddy smart collar is a LED-capable collar that can track and monitor your dog while the DOTT dog tag is a Bluetooth-enabled device that attaches to a dog's collar and pairs with the owner's phone to form a virtual leash. When it comes to cats and feeding, the CatFi Box is a low-tech feeder that helps track your cat's eating habits while the Bistro Cat Feeder is equipped with facial recognition technology to help with portion control.