
All of my dogs, save one, learned to use a dog flap simply by showing them how it works and then gently coaching them through it the first time or three.
My Rudi was the exception, he is very noise sensitive. On his first visit to my home I showed him the flap, opened it slightly and he went through it with no problem. Later on his breeder/owner and I were standing in the kitchen (where the dog flap is) with Rudi. Abby (my other dog) came zooming through the dog flap like a torpedo. The flap shut with a loudish clang and from that moment on Rudi was afraid of the dog flap.
A few weeks later Rudi came home to live with me for good. Many months later and £160 pounds poorer I invested in a flap which makes virtually no noise. Sat it in the living room so Rudi would familiarize himself with it. Spread pate on it. Lick, lick. Stuck chicken where the door opened -- Rudi would not go near it. Installed the dog flap in the door .... one month later I got fed up with every positive reinforcement technique in the book, Rudi was still terrified. I shoved him through the door. Eventually he accepted he had no choice. After a couple of weeks he worked up the courage to go through the flap himself, with me standing ready to eject him. :-) Shortly after that he was zooming in and out of the flap by himself at top speed. Would I recommend this approach ... never!
As to home insurance - the flap I bought is heavy plexiglass. It has a key that allows you to lock the flaps. In addition, if you are away for an extended period of time there is a steel plate which slides into the opening and screws closed from inside the house. It's more secure than any of the windows in my home.