Command & Conquer: The Covert Operations Cheats & Tips

In some missions the enemy will have the ability to call in Airstrikes, which they will do every several minutes. They will always target your northenmost building, so a way to avoid collosal damage to your base is to build a line of sandbags north and put an inexpensive building there, such as a guard tower. That way if (or rather when) it's destroyed, you lose $500 worth of building rather than thousands of dollars + units from your main base.

You can attempt to protect it by surrounding it with Rocket Infantry, SAM Sites (if you're NOD) or Mammoth Tanks/Advanced Guard Towers (if you're GDI) but there will usually be 3 planes to shoot down and it takes a lot to bring down one plane, so you're often just better taking the damage and replacing the building.