This will prevent any Spy from moving deeper into your base, because if the buildings are close together, they will set him to uncloak. Also, Include Guardians, HLT's and Defenders amongst your buildings, so that when and if a Spy does become visible, they can take it out before it discovers anything of importance. This usually means there is a spy in your base. Takle it out, look for others, take them out, look for the spy, and take out the spy. Have Peepers patrol through your base.
Aircraft can reveal a spy just as good as any other unit.
Because they move quickly too, they are really hard to dodge. Look for an enemy blip in your base or near the edges of the map. Contact us for more information on GameSpy Industries.