On our Jeep Liberty, the ignition key had to be left in the vehicle, as Jon stated, in order to keep the steering "un-locked".

Since the ignition key for the Jeep Liberty is "chipped", I purchased a blank key cut to fit my ignition, and that's the key I left in the vehicle while towing it. The blank would unlock the column, but the Jeep couldn't be driven. The engine would shut down without the properly coded ignition key.

Now, convincing the locksmith to make me a key that we both knew would be useless to to actually drive the Jeep is another story...