For safety, have a companion hold the bottom of the ladder. If you don't have somebody to accompany you, you may always use a sandbag or something else substantial to keep the bottom of the ladder in place. This allows your companion to take over if needed. You can also use a harness for this purpose. Attach one end of the harness to the ladder and the other end around your partner's waist. Now your partner can stand behind you while you climb up the outside of the building. Finally, you can always use a rope to sneak someone up a wall. Tie one end of the rope to the doorknob of a room where no one will be during your climb. Then, pull your partner up after you are done climbing. That's all there is to it! Sneaking up someone is very easy if you know what tools are available to you. Have fun sneaking people up!