So, earlier today, I’d finished cleaning out Theodore’s litterbox and replacing the litter and hay. While I was cleaning, this little spritely fellow was doing some crazy Bunny 500s in his pen — the extra space while the box was out probably encouraged him to do this. He’d sprint the whole width of the pen, stop quick, look at me like “Did you watch me?!” and then turn on his heels and do another 500 the other way, then stop, give the same look, repeat. Adorable. Then he hopped around a bit and explored for a moment until I replaced the box. He’d gotten a lot of exercise in that short amount of time.
I went to the other side of the room as I often do and sat down in the armchair. He hopped to his box and started munching on the new hay in the box and basket.
Then, after a minute, I realized I couldn’t see or hear him. So I sat up a bit and saw what looked like a flopped bunny body in the litterbox. Panic-stricken, my protective brain immediately jumped to the thought that he’d had a heart-attack. You have to understand, Theodore has never lain down in his litterbox before.
I rushed over to the pen to see this:

And he would turn his head to continue munching on the hay. 
It’s funny – Theodore is my first rabbit, and there’s still all these things I’m learning, like the fact that his attitude changes a little during his molt (which he’s currently in), and his interests change from trying to chew the side of the chair to trying to chew the carpet – from jumping into the supply shelf to ignoring the shelf and jumping into the bookcase. 
So I’m not really worried about his decision to flop down in the box today because I know that’s a normal bunny thing, and he only did it for a few minutes before he got up again and sat normally to eat, but I am concerned he might make a habit of this and become completely drenched in urine.
Any thoughts towards preventative measures? I was thinking a screen, maybe, if this becomes an issue.