Hey after me and my brother designed a section of the world that is entirely based on keeping the Tarrasque dead. After designing it I was wondering how others world build with the Tarrasque. So how did you world build with the Tarrasque? 

The Tarrasque can certainly be killed, and it would be an epic battle, indeed it would be legendary.  Stories of it would be told for generations.

Keeping it that way?

Legendary Destruction. The destructive potential of the Tarrasque is so vast that some cultures incorporate the monster into religious doctrine, weaving its sporadic appearance into stories of divine judgment and wrath. Legends tell how the Tarrasque slumbers in its secret lair beneath the earth, remaining in a dormant state for decades or centuries. When it awakens in answer to some inscrutable cosmic call, it rises from the depths to obliterate everything in its path. - so it says in the Basic Rules Compendium, on page 250.

Can't say I've ever done anything with the Tarrasque myself.

In one of my worlds,The Tarrasque was created by the mad five (Insane and endless powerful wizards many long dead) working together.The tarrasque ultimately played a large role in the end of the world but was killed by uralter who sleeps forever after the battle.

Assuming you can't KILL the tarrasque but only defeat it and send it back to sleep...

If it's an old world (e.g. has experienced and survived a previous attack) I'd probably have the tarrasque at the centre of a vast containment facility maintained by most of the kingdoms/nations of the world in a collaborative effort.

It would all be for naught if the beast woke up, but that's how I'd do it.

I had designed a "Dagger of Eternal Slumber" which essentially made any creature which was pierced with it sleep for as long as they remained pierced by it.

The players would find the dagger embedded in a solid bone alter underground. If they removed it, then the alter would pull itself into the ground and reveal itself to be the horn of the tarrasque, now waking up.

The idea was to put this on the party when they were feasibly powerful enough to survive but not powerful enough to kill the tarrasque. It would turn into a puzzle to re-embed the dagger into the Tarrasque.

In my homebrew world, the tarrasque was one of the first beings created by the gods, in an attempt to create life that would sustain itself. However, like its predecessors (the aboreon/proto-aboleths and the krakens) the tarrasque could not reproduce, even though it was immortal. After its creation, the tarrasque rampaged across the globe, even creating a lake, and its creator, a primordial deity named Brogon, was forced to seal it far under the earth, for fear it would destroy more of the gods' creations. After that, the gods chilled for a thousand years before they made the dragons and the giants, the first creatures that could reproduce and expand as a species.