Even though I keep a password on my phone, there's still plenty of opportunity for my son to destroy it. Any time I put the phone down on a table or lay it down next to me on the couch, he can run over, grab it, and start banging it against the wood floor, just to see what kind of sound it makes.
Fortunately, there are many rugged phone and tablet cases that can take a licking and keep on ticking. Lifeproof, Ballistic and Otterbox all make extremely sturdy cases that can withstand a serious fall or even a dunking. For example, the $80 Ballistic Hydra case for the iPhone 5 can survive an 8-foot drop or 30 minutes under water.