I never ever build my second base right next to my first, because if a mass army is going to destroy your first, your second will most likely be destroyed as well. Is this a good idea? I've noticed this quite a lot, how my foe will usually check right beside the first base, then give up temporarily and re-build lost units.
This will only work against bad players. Hiding an expansion far from your base is a cheesy tactic that relies on them not scouting.
If you build your first expansion at the natural (nearest your main base), then the enemy shouldn't be able to destroy either because your army is able to defend both. If your bases are too far apart then the enemy will be able to do damage to your bases even if your army is weaker than theirs.
