Ignore everyone else's comment. So far, all the other answers they gave is bs/excess noise.
REAL ANSWER:
The card's ability is a double-edged sword. You'll have to use other cards, i.e. traps and spells (such as the aforementioned "guardians") to keep it around.
That said, there is a high levels Gaia Monster card that has a 'quick-effect'; that will tribute the fusion spell to summon it.
Ideally, you're supposed to use the Gaia fusion cards rubbish effect to reduce the opponent's attack, and tribute it with a quick summon 'Soldier Gaia', and 'then' attack the opponent's monster for 2600 points of dmg…
What's more, the 'last'effect of fusion card (Gaia the Magical…) is more useful.
When it destroys an opponent's monster, it gains a solid 2600+ PERMANENTLY. This is when it's risky ability should be used (to remove dangerous cards, e.g. Alter-BEWD).
Anonymous
Hawk
