Correct answer is When the gust lock is on there is protection to prevent take off.

If its an external device that is fitted on the ground then there is no inherent protection, other than painting it a bright colour and puting a 'remove before flight' flag or legend on it.

However, where an integral device is used (i.e. some sort of lever or latch on that is moved to engage / disengage the lock) then (on a modern aircraft anyway) this will be positioned in some manner that you can not take off if it is still engaged.

Example:

ATR series turboprops. The gust lock is a T shaped handle in between the power levers. When it is disengaged it sits at the front of the range of travel of the throttle quadrant. Before it will engage, you have to move it to the rear (i.e. pull it back towards the rear of the aircraft) until the T is a little way in front of ground idle. You can then engage it (a push downwards, with the control column central IIRC). Now, the protection here is that each arm of the T extends laterally in front of one of the power levers.

Hence you cannot advance the power levers to take off because the position of the gust lock prevents it. All you get is a little bit of forwards movement, enough to taxy, but thats it.