Our 3 year old Pomeranian has been with us since he was 4 months old,
and ever since we got him he's always made a big fuss about us leaving
him alone in the apartment. (and sometimes if we leave the room at the
same time he gets upset)

We can't seem to get him to stop barking. As far as we know he barks
constantly for up to an hour after we leave and then stops.

But today we got a call from our apartment manager asking us to
contact them because they heard him barking while they were showing
another apartment.
I know they were showing the apartment just as we were leaving, which
is why he was barking so much.

We've never had our neighbors complain to us or them and we've been
living here for almost 3 years now, in two different apartments at the
same complex.
But I'm really worried they're going to tell us we have to move/get
rid of our dog if he won't stop barking.

The barking is only really a problem when we leave him alone in the
apartment. We've tried leaving him in his crate, but he scratched the
door and whined so much that we never actually left the apartment with
him in there for fear he's hurt himself.

Any ideas?