AFAIK they don't yet make a microchip flap in dog sizes. However it would be a pretty brave burglar to stick their head through a dog flap into a house with 2 unknown hounds
Squidge was waiting for me to throw her ball on that pic. They both seem to have mighty long tongues though!
It is surprising how small a flap you can get away with, mine is a medium which would not accomodate the shoulders of an adult person, they would have to send a kid in first and since all my doors are mortice locked and the keys are hidden, they wouldn't be able to get all that much stuff out through the flap
If I was ever away for long and took the dogs with me then I would simply lock the flap and set the house alarm. I cannot set the alarm with the dogs at home unless I cover the lounge, dining room and kitchen sensors so I generally don't bother!