"Realize that no plan survives contact with the enemy, and simply improvise." - yep, thats about it for me. Realize that any efforts of NPC's the party is trying to detect and thwart may have been anticipated - equipment them and their allies with ways to block, foil, or misdirect some of the efforts and powers of the PC's. Its not cheating, its just playing them smart - especially if some plot is well planned and financed.