Santa Pony Mainly, ponies are difficult to hide in an apartment. The usual places don't really work.
Behind the couch? It might be wide enough, but not tall enough unless the pony is sitting down all the time. Naturally if the wife is sitting on the couch, she may notice pony sounds coming from inches away. Also, hay makes the wife sneeze if it's right in her face.
Do ponies sit down?
Conclusion: Probably won't work
Closet? The issue here is that of course we only have ONE closet. Granted, it's large and divided up between HIS and HERS, but there really isn't a way to keep the pony on my side and not have it walk over to her side and maybe nibble on her shoes or sweaters.
Also, since we don't have a closet door but use a very attractive curtain arrangement (stolen from Mina years ago) whenever the pony flaps his tail around or moves, it's obvious that something is in the closet that isn't clothes, shoes, slide projectors, nerf guns, or ice skates. It's tough to explain that away when the wife asks what's in the closet - even worse when she thinks that it might be a closet monster.
Conclusion: Best situation for the pony. Would have to move a lot of stuff around.
Under desk in office? See, that is what I was thinking as well. There is plenty of space under there since I finally got rid of that extra dot-com era computer that was taking up space. Unlike the closet, this space is wide open so she would instantly see a pony if it was under the desk. I suppose the trick would be to get a sheet or table cloth and put it on the table. Of course, she would suspect something then. On the plus side, I can always blame any pony noises on my computer.
Conclusion: I'll need to cover the desk, but this could work.
Under Bed? Our bed is really tall. Like 100 feet off the ground and we have to use one of those gymnast spring-boards to get into bed. The pony could fit under there, but he'd have to sit down the whole time and the constant bales of hay right under the bed all night would drive her sinuses crazy. Any horse-like noises during the night, much like in the closet, would be hard to explain although I could always blame it on our neighbor, Stompy McFartster.
Conclusion: Pony may have nightmares and start bucking around.