Not dumb, that would be a "kill switch". A lot of people use them. It's a low cost thieft detterent, does not stop them all together, but it's another tool.
A number of ways to do it, cuicuits to interupt.
Don't make the switch obvious. Switches usually don't go bad if they are lightly loaded, but know where it is so you can grab and splice the wires to bypass it.