Got a fuse on the long battery cable? If your required shutoff is in that cable, better get to it quick if the cable shorts to the frame. Also keep it away - well away - from any fuel lines. Also, if you have nice equipment in the car like a stereo or high buck ignition and such note that cutting the positive cable with the engine/alternator running may/will cause a power surge in the car that could damage equipment. Also, an alternator car likely won't shut off and you will fail tech. Also - in my experience - the long run from the battery to the solenoid can cause slow crank due to voltage drop, unless you use pretty good sized cable and really watch your frame grounds.
I use a 4 way shutoff and break the power and negative at the same time. I also put the solenoid in the trunk so that the start power is dead unless cranking. Alternator feeds the battery directly and when the power is cut any excess energy hits the battery only.
My basic layout