Figuring out when she wants to come back inside has been a bit more challenging. It was always hard to tell if, when I opened the door and called, "Lily, wanna come back inside?" she was coming back in because she wanted to, or if she was just doing so because she thought I wanted her to. Even her sitting or lying by the door wasn't necessarily a clue, since she seems to just like to do that sometimes even when not ready to come in. Generally I would figure it out one way or the other only by her wanting to go back outside again just a few minutes after coming in.
Recently, though, Lily has furthered her communication skills and started scratching at the door when she wants to come in. She does it very politely, just a gentle "scratch-scratch-scratch," and then a pause to wait for someone to come let her in. If no one hears her the first time, she resumes the scratching and pausing pattern until someone arrives. It's really very convenient, taking the guesswork out of the situation for me. I'm quite proud of her for implementing this new system all by herself. Although I do have a friend whose beagles literally throw themselves at the door when they want to come in (flying beagles!) so I hope this isn't a slippery slope...
How do your dogs communicate with you about their desire to go in or out?