I do believe that most theft is opportunity driven and few carry bolt cutters or heavy wrenches around to twist off something. That is unless they have seen your rig often and are just waiting for the 'right time'. I have seen rigs around town that have no anti-theft protection whatever as the hi-lift is located in a position that would make it less than instantly available to a would be thief...but then it also makes it less than desirable for the owner to use it themselves.
Running a lock through the bolt and handle might work but would always have to line up to be effective.
Most locate them behind spare tires (many jeeps) and some on the hood as well. Those with bull bars or ARB type bumpers mount them on the bumper, some on the roof rack on one side or the other with their shovels and ax.
I have thought about a cable too. Still has to have a lock of some type or a lock similar to the kind used to pass through the shell carrying (magazine) part of a rifle, but those don't look to sturdy for this type of application.
Oh yeah, don't lose the key!!!