The guy who made that rule (Jeff Cooper) says this on the subject of rule II "A firearm holstered properly, lying on a table, or placed in a scabbard is of no danger to anyone."
Rule 2, the expanded version "RULE II: NEVER LET THE MUZZLE COVER ANYTHING YOU ARE NOT WILLING TO DESTROY
Conspicuously and continuously violated, especially with pistols, Rule II applies whether you are involved in range practice, daily carry, or examination. If the weapon is assembled and in someone's hands, it is capable of being discharged. A firearm holstered properly, lying on a table, or placed in a scabbard is of no danger to anyone. Only when handled is there a need for concern. This rule applies to fighting as well as to daily handling. If you are not willing to take a human life, do not cover a person with the muzzle. This rule also applies to your own person. Do not allow the muzzle to cover your extremities, e.g. using both hands to reholster the pistol. This practice is unsound, both procedurally and tactically. You may need a free hand for something important. Proper holster design should provide for one-handed holstering, so avoid holsters which collapse after withdrawing the pistol. (Note: It is dangerous to push the muzzle against the inside edge of the holster nearest the body to "open" it since this results in your pointing the pistol at your midsection.) Dry-practice in the home is a worthwhile habit and it will result in more deeply programmed reflexes. Most of the reflexes involved in the Modern Technique do not require that a shot be fired. Particular procedures for dry-firing in the home will be covered later. Let it suffice for now that you do not dry-fire using a "target" that you wish not to see destroyed. (Recall RULE I as well.)"
