Help, Please!

The other day I *sat* SB in his crib for a minute while I took his diaper into the bathroom... this is what I saw when I came back! Since then he has nearly perfected his skill of standing up. However, there is one little problem. I snapped these photos which document his standing process perfectly-- here's how it goes:

I put SB down for a nap or for the night (sans fishing hat), and as soon as the door closes, up goes Sean.

He's so proud of his new skill. for a few minutes he stands and smiles at himself, surveys the room, bounces a little, giggles a little.... wonders what to do next.

Running out of things to look at and giggle at, he usually starts biting the side of the crib. This would be okay except for the two new teeth he has. The other day I put my head in the crib and found all sorts of two-pronged scrape marks along the inside rail. The paint has actually been scraped off... where does it go?

Now the tough part--- after exhausting his stand-up entertainment, he either (a) wants to lay back down, or (b) wants Oli or St. Francis. The problem is he can't sit back down! So he will stand and reach and reach and reach, to no avail. He just can't let go of that second hand to let himself sit down. And he gets stuck standing.

What was at first fun now turns into a panic-ridden scream-fest. He's stuck. He can't get Oli. He can't sit down. His legs are tired. He's scared of falling. I'm scared of him falling. And so he stands there screaming until one of us goes in his room to help him down. First, I hate going into his room when he's supposed to be sleeping. Second, after I lay him down again and leaving the room, this is what happens:


And so we begin again! He will do this until he tires himself out so much that he can't pull himself up anymore!

Any ideas about (a) how to teach him to let himself down, (b) how to get him to stop biting his crib rail, especially since i'm not going to sit in his room his whole nap, and (c) how to get him to stay laying down after I leave the room?