Now that you are familiar with simple queen forks, consider a first way they can become complicated: the square you need—the forking square—might be protected. “Protected” does not mean there is an enemy piece on the square, of course; it means there is an enemy piece attacking the square—perhaps defending a piece that sits on it, or else just protecting it while it is empty. In either case, here just as in the chapter on knight forks we will see that an exchange often eliminates the problem. Perhaps the defender itself can be captured; perhaps the piece sitting on the square can be captured, so that when its defender recaptures the square is left unprotected (with its former guardian now sitting on it); or perhaps the defender can be lured away by capturing another piece it protects or making a threat (e.g., a check) that requires the guardian’s services elsewhere. Since the basic theme is familiar from the chapter on knight forks, we will look more briefly at examples of how it works here.
Examine the position to the left using the approach already established: look for ways to combine a check with an attack on an unguarded enemy piece. Here you see that Qd5 gives check and also threatens the loose knight on a5. But before you make the move you also have to ask whether—and how many times—the needed square is protected. In this case it's guarded by the knight on f6. So: do you have any pieces attacking the knight? Yes, the bishop on g5. The idea behind the resulting sequence is familiar from the chapter on knight forks: 1. BxN, QxB; 2. Qd5+, and White wins the knight.