Toddler Sleep

Our son turned two in April. He has been in a toddler bed for a while and for some time now right when we walk away from his bed he gets up crying following us, lays down behind his door, cries some more and falls asleep there. Even when we fall asleep beside his bed, right when we get to the door - its like he just know we are leaving and does it. We have tried the "100 walks" and even putting him back in his crib. That didn't work. At all. We have baby two coming in December and really want to get this straightened out before then. We would love to hire a sleep consultant but just can't afford it.