While most of you recognize I've posted this picture before "with a laugh" in mind, I REALLY believe this is the only way to protect your cars.
The two things I've done with my truck is a "buried" kill switch AND a hidden fuel shut-off vavle.
As for the trailer, I bought two measured lengths of REAL hardened steel locks and chains (not the HomeDepot kind), but the kind that has to be aceteylen torched to cut and locked both left and right rear wheels together. If you're not up to this, then sleep in your truck/trailer with your gun.....
Jeff x 2