My sons will come to whoever he deems important enough to let him out and bark once then nod towards the door. If you don't jump right away he will do it again then he goes and stands by the door. Keep him waiting and he'll start scratching. He doesn't get that we can't drop everything at his moments notice to let him out.

Ours usually runs to the door, and sometimes barks or whines if it's been a while (like when everyone's sleeping)...but lately he's taken a liking to going in the house because my mother's boyfriend intentionally ignores him when he asks to go out.