Not sure if this will help but I was Reece’s 3rd and final family as well and he was 4 months when we got him. I found that no amount of walking would stop the accidents and soon discovered that Reece associated walking with play time. As soon as I started leasing him in the backyard he began to change his behavior and learned that outside was potty time. It’s quite possible your pup doesn’t realize that walking = potty time. Good luck!