Battery isolater

I want to isolate the battery just for a bit of extra security . I thought on the NEG cable . Do i jump the switch with a 5amp fuse to keep the radio presets . Im not likely to switch it off with the engine running , But if it ever did i don't want to fry the alternator . What is the way around this , Switch the POS .
I did have a small key switch on one of the ignition wires , in fact 2 of them but it was a right pain faffing about with them , So ive taken them off but want to put something back on . I have a Lucas isolater so would like to use that .
I don't want to start wiring fuel pumps etc , i just want something simple .

I did the positive with a jumper fuse, no problems.
I've used a resettable fuse though cos the Doris kept forgetting the isolator key and popping the blade fuse.

Hi , ive just been looking at the resettable fuses . So switch the POS in the battery box (easiest) . What about this alternator destruction problem if turned off . Its not likely as its only me in it ,

ps what size fuse . 10 or a 5 amp

5 amp in mine but I just guessed that's what I needed.
I think my iso switch has been knocked to off whilst driving maybe 3 times and I'm still on the same alternator.

I used a flush mount fuse holder fitted in the front of the seat box, it means cutting a rectangular hole but it looks neat.

This comes with a device to protect the alternator. Whether you can figure something similar to use with your Lucas switch?
https://www.12voltplanet.co.uk/battery-isolator-switch-removeable-key-with-ignition-isolation.html

Thanks for the info , i thought 5amp . but will jump the switch as its an automatic reset fuse no need to touch it and im thinking of the blade fuse inside the box , not mounted
Will check out the device to protect the alt , But sounds like i may get away with it .

switch looks good , but the wiring diagram is a bit confusing , well to me . No coil for one .

If it wasn't for the Doris I would have left mine inside the seat box.
Edit- just re read and see your fitting an auto reset one, with hind sight I should have done that.

Hi i switched the POS in the battery box and did the bridge trick 5 amp fuse . All appears to work ok .

So if i now take the wire from the ALT to the starter off the STARTER , And run the ALT cable direct from ALT to BATT , will that stop the ALT destroying itself .