Our 7 month old has easily learned to ring the bell when he has to go potty, but now he's using it to just go outside. I'm stuck on the discipline action here.

He's basically using it for attention, but I'm telling you he doesn't lack it at all. The last thing I want to do is punish him for ringing the bell, even though he just came back in.
He runs 4-5 days a week and I also am training him to retrieve, so it's more about getting inside his head to let him know it's not ok to go outside on his terms.

And yes, he's always on some sort of lead when he's outside, even for bathroom and training.