we would put my son back in his bed over and over.he finally got the idea. he was 2 1/2 when he was put in a twin bed from his crib.
maybe he is too young and not ready for a bed and not a crib(?)
i'm with another post. i'm not comfortable with closed doors or locking doors. i still have a monitor in my almost 3year old daughters room (who is still in a crib b/c she is so small and can still fit in one..lol) so if he or she gets up i can hear both of them. we partially close the doors but leave them half open so they know we are always there.
i have heard of doing that, locking the door and letting the kid cry till they fall asleep and some moms would find the child at the door asleep..that would just break my heart too much.
compared to many stories i hear i'm probably pretty darn lucky when it has come to sleep with my two.
i would say if he is too big for a crib and you don't want to try a crib tent( if he is climbing out),, then the gate at the door would be a good safety device that would still give him the feeling you haven't locked him away with out any contact from you.
good luck