It's been a while since I've tried a new Spanish word to teach Wally. I decided to look up "inside" in Spanish, and the word that popped up is "adentro". Outside popped up "afuera"
With how often I call him to come inside and go outside, these might be words he picks up quickly.
The way I'll likely teach is pretty much the same I taught "inside" and "outside". I say the word and then use a hand signal to direct him in or out.
This time, though, I will try to take it to the step I never bothered with for "inside", "outside" - teaching him that each means a certain thing. For example, coming from outside to in the house is only "adentro". If I say "afuera", and he comes in, that's not right. I don't let him in.
And of course, the reverse - "afuera" is going from in the house to outside. If I say "adentro" then he can't move. If he does - he doesn't go out.
This is will be an interesting twist. I'm not sure why I didn't try it for "inside" and "outside". I couldn't tell you. Maybe I didn't think of it at the time, and then just figured to let it go.
But this time (once I learn how to say the words consistently myself) we'll go all the way with it, or at least try it.