That's called an isolation switch. The best is how you have it in your diagram - ie, the top right isolator in the ground - although it's usually a switch, not a (single) relay.
That battery -ve to to chassis/body/engine switch isolates battery power from the rest of the vehicle vehicle.
What I said was that that will not KILL the engine if it is running.
A Kill Switch kills (stops) the engine.
An Isolator (switch) isolates the battery.
They are two different functions (though some IMO silly people try combining the functions for general use).
Usually fuses or circuit breakers are used to protect from shorts - not switches.
And as I hinted, if an "isolator relay" unintentionally opens....
Why not say what you hope to achieve, why you want to do it, and under what circumstances?