How do I get my dogs to stop pooping and ****** on the carpets?

we have 2 yourki poos. they have a doggie door, and they use it, but they prefer to use the bathroom on my carpet !!!
We clean our carpets with a carpet cleaner once a month. The dogs cont. to go on the floors. What can we put on the carpets to prevent them from returning to the same spots daily !! I wont ***** them and we never catch them in action. We lock them outside in the morning for about 15 minutes, they still hold it until they return to the carpet. It only seems to be happening in the morning !
Short of putting them in diapers, I dont know what to do….. Help

Marietta Carpet