The way I like to do it is like this:
You will need:
Switch of your choice (toggle, etc)
Maybe 10 Feet of wire (Leaves room for sneaky wiring)
Two flat male wire connectors
An in-line fuseable link
Wire nuts
First, find and remove the"IGN" fuse. Now Attach one flat male connector to one end of the wire and plug it into one side of the ign. fuse space. Now add the fuseable link and put the fuse in it. After the link comes the toggle switch (or any other switch of your choice). Run the switch to a hidden location known only to you or trustem family members. Run a length of wire from the other prongs of the switch back to the fuse location and plug the other male connector into the other side of the IGN fuse space. And voila, kill switch.
Get creative with the kill switch location. For my brothers previous car, we wired a switch that had to remain pressed (sorry dont know the term) and connected it to the park break release. So you had to keep the break release pulled to start the car, very very sneaky. The car will crank all day but isnt going anywhere. If anyone disagrees, please let me know, this is just my way of doing it and I dont want to give out bad advice.