Sounds like a good idea. I have often wished mine would "cover" less ground.

The only way to retrain them would to be there with them on a leash every time you take them out to potty. They would have to understand that this area is for this purpose. If you don't praise like crazy as soon as they do what they're out there for, they won't get the message. Once they potty, you can let them off leash to play. If you just put them in a pen and leave, the message is lost. This means EVERY time.

Eventually they will be able to be sent into the yard and they will go where they should. But it won't be immediate.

Mine have access to the yard all day while I'm at work (doggy door) so I would have to close off the door and retrain 3 old dogs of 12, 13 & 8. Not gonna happen here.

Good luck.

Mary