Got a new puppy last week and he seemed to be getting the idea of weeing outside not inside. But today we had him on a lead which allows him to go in and out of the open front door. He kept going inside to wee - any idea why? Other than regularly taking him out, saying no if he tries or does wee inside what else should work?
We got our 4 yr old as a pup but he just seemed to learn in a few days (bar occasional night misshaps).
(Also I'm abroad so we don't need to keep pups inside.)
Because he doesn't know any different? He needs loads of praise when he goes outside, and for any accidents inside to be ignored, and cleaned up without reprimand. There are loads of threads in here with house training methods pasted in, have a search Are you sure you aren't looking back on your old pup with rose tinted specs?! Most puppies take far longer than a few days to be fully housetrained. I think mine was nearly 6 months before the accidents stopped completely.
As well as praise you will really speed up learning if you add in a high value treat each time they go outside. Ignore if they go inside, you don't want to teach them to be worried about going in front of you. It's also helpful to teach a command by saying it each time they go. You were very lucky if your last pup trained itself without any positive reinforcement for going outside.
I think having free access to outside will confuse him tbh. Initially I would take him out every half an hour or so and reward all pees. For me it's better if the dog learns to ask to go out initially rather than being able to get out unhindered because you need to plan for the occasions when the door is shut. It's only now that Eric is house trained (has been from about twelve weeks) do I leave the back door open if the weather is good, mind you he still comes and tells me he has pee'd.