I'm with Greg on this one.
No matter what you do to prevent a thing like this from happening, some idiot will always circumvent the system and come up with an even stupider means to an end.
Personally I'd never get up on the top of a Fire Engine in the first place, you'd look stupid if the thing took off with you up there.
I take it you mean the overhead service to your house, is the wiring you are talking about.
As long as the wiring is insulated for Full Working Voltage, I don't see a problem.