Hi Milky911,The posts above are all good idea`s,but the best way to do it is in layer`s,pedal lock,clutch pin,removable steering wheel,cut out switch,and a tracker,if you really want to keep it,you`ll do a few of them.
Will French on Facebook runs a company that will give you all the info you need,he`s exceptionally helpful,even if you don`t purchase a product off him,also i`ve just found a Tracking Website (I have no connection to it),Called classictracker.co.uk,who are having a sale on there safer Tracker till the end of October,where you can pay for there middle option,of Tracker @ £199:00,for a yaer,instead of £299:00,Nick the owner is very helpful also,I advise you to check them both out!!!
Above is the link to the Facebook site of Land Rover Defender Security Awareness,I hope this is of some help to you??? All the very best my mate,Lee.