Nothing will stop a determined thief, all you can do is make it difficult to steal, hopefully so difficult they will move on to an easier target.
Insurance, as mentioned above, might be worthwhile but be certain that the annual cost truly provides coverage of the true value of the vehicle. Insurance companies notoriously try to pay out as little as possible and will depreciate vehicles based upon age. Rates may be so high that insurance isn't worthwhile and some insurance may not cover accessories you add.
If you are going to try to lock it up outside I suggest a few methods to make it difficult for thieves.
1) A poured concrete base as mentioned above with a loop of steel as large as possible in cross section to prevent hack sawing or cutting with bolt cutters. Use large square link case hardened chain which will damage bolt cutters and resist saws and a lock that has high resistance to those same tools. Placing a lock inside a welded steel box can make it more difficult to defeat. Place the concrete tie down so that when the Ranger is parked it is over the top of the anchor so it will be difficult to dig out or use tools to cut the chain. Of course these provide little protection from a cutting torch and today with cordless reciprocating saws the job of thieves is easier.
2) Light the area well with a light that is high enough that thieves cannot break it and one that cannot be disconnected easily.
3) Keep the vehicle inside an enclosure with a high chain link fence that allows little room for thieves to work on your security features.
4) Make the vehicle undrivable by disconnecting the fuel pump, removing a tire/wheel, removing the battery or a boot that secured the tire/wheel so it cannot roll. Use one or any combination of these methods to dissuade thieves. The problem with these methods is that you can't just jump in and drive off when you're ready to use the vehicle. That measne something as simple as flipping a hidden fuel pump switch or something as complex as replacing a wheel/tire you've removed.
5) Thieves don't like noise or attention so an alarm of some type that sounds loudly when someone enters the chain link enclosure. Of course the alarm will need to be discreet and difficult to disable so thieves won't be able to inactivate it.
6) Out of sight, out of mind applies for thieves that might be out for a crime of opportunity. If they don't know you have it they won't try to steal it. If possible keep the vehicle in the back yard out of sight from passers by, and close to the house, maybe close to a bedroom window. The idea of being caught or shot from a bedroom window might dissuade less determined thieves. Build a small shed to keep it out of sight, add a layer of security and also keep it out of the weather and away from varmints.
7) Security cameras well placed out of reach with clearly visible signs telling would be thieves that the area is under surveillance. At best this is a deterrent and might help authorities catch thieves after the fact and help convict them, but it won't stop those who use methods to obscure their identity.
