How about a "drown proof" pool.  When this pool isn't it use, people don't even know you HAVE a pool. Basically the bottom of the pool comes up to the top when you're not using it.  Not only that, but you can have it come up different heights for different uses. Click through for a VERY cool video.

I like this pool idea even better than a pool with a retractable cover.  Heck, you could have someone die in the bottom of this pool and just push a button to bring them to the top.  Check out this video of the coolest pool in all of pooldom!