My L3710 had a backup mechanical shutoff. After reading this post, I got out my L5740 manual and it says that if turning off the key doesn't stop the engine, call your dealer. Interesting. One, my dealer is 150 miles from me. Two, they aren't open from noon Saturday to Monday morning. Wonder why they don't give some recommendation for shutting it off, like blocking the air intake or cutting off the fuel some way.
At Caterpillar, the machines I worked on had 2 system types - power to run and power to shut off. On the power to shut off we were required to have a mechanical means to shut the engine off if the power shutoff failed, but that was probably an internal standard. On one machine it the mechanical shutoff wasn't easy to reach so I suggested writing in the manual, "If the engine doesn't shut down, place your cap over the air intake" but the safety group wouldn't buy that. We had to come up with an auxiliary mechanical fuel shutoff valve that was easy and safe to reach.