I don't know about you, but animals don't seem to last very long in my games. Often it seems that the moment somebody gives them a name, it's just a matter of time before they croak.
Take Bagsy, the loyal mule eaten by goblins after being left alone outside the Keep on the Shadowfell. Or Stumpy, the trihorn behemoth burned alive in a reckless fire started by our warlord (Stumpy actually survived with extreme burns, which made it kind of worse). Or the "small but vicious dog" listed under the Rat Catcher's starting gear in Warhammer: I've probably seen more of those kick the bucket than actual rats! Over the years I've lost count of how many riding horses have been crushed by avalanches, ridden off cliffs, or just caught on the wrong side of a fireball - and don't get me started on familiars.
Of course, I'm to blame most of the time. Killing a pet is probably just a cheap way to crank up the pressure, so I end up treating them like red shirts, or those rookie cops who're just about to get married. Perhaps I'm just haunted by a scene from My First Ever Adventure (I was nine!), when my brother's character asked a local woodsman if he'd seen his horse, and the DM told him the guy was wearing suspicious-looking horse-ear slippers - a stroke of genius that I've possibly been trying to emulate ever since.
Still, sometimes it's just down to the nature of the game: D&D has lots of explosions, and animals are usually pretty frail. Which is great if you just lurve killing animals, but sucks if you want to play a classic "man and his dog" concept. Thankfully 4th Edition is quite good at abstraction, so it's easy enough to come up with a set of rules where they simply can't be hurt. So long as your loyal companion isn't a fighting dog, I think it's fair to give them a handful of flavourful utility powers, yet keep them pretty much off-map during combat (incidentally, this sort of thing is one of the reasons some people hate 4th Edition - but let's not go there thankyouverymuch).
Check out the rules below. It's a matter of taste whether or not you demand a feat to get these powers, or just hand them out willy-nilly. I'd be inclined to go for the latter, so long as the player invests some time bringing the animal to life at the table.