How to secure a ladder

A few weeks ago we had our bedroom window replaced (a topic I'll cover in another post soon), and the guys who came to install the window used what seemed to me to be a very clever trick. They held a full size crow bar against the bottom rung of the ladder, and hammered the straight end into the ground like a tent peg so that the foot of their ladder wouldn't slide out from under them. 

Do you think that this is another great use for the woefully under-appreciated crow bar (see Ode to the Mini-Crow Bar), or a dangerous recipe for disaster?

Would it be better to hammer the crow bar in until the curved part hooked right over the bottom rung, or does the way that they have it work just as well?

Or should we just stick to doing things the old-fashioned way and make sure that we have a friend on hand to hold the ladder in place?