I take my car key with me, no fob.
For extra safety, you could temporarily disconnect your battery while you're on the trail. This will deter most amateur thieves.
Another option is to leave your key hidden in your vehicle and use a club on the steering wheel which takes a smaller, lighter key or a combination lock, like this one.
Whatever you do, don't leave anything of value in your vehicle for other people or for animals.
Hope this helps. Cheers!
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"Without craftsmanship, inspiration is a mere reed shaken in the wind." - Johannes Brahms