Ghost

We have a great pyrenees we adopted a few months ago and while he's the sweetest dog and we love him he has the issue mentioned in the title. He doesn't want to hurt anyone he just runs up to/in front of them and barks at them. If they happen to stop he just barks at/sniffs them. Since he's a pyrenees I'd imagine this probably stems from the big protection instinct typical of the breed, as when we very first got him this didn't seem to be an issue. He usually just stays in the yard and lays down or hangs out by the corn field/pond otherwise.

It's hard to teach him cause since we live in the country people only pass by on foot/bike a few times a week and we obviously don't know when exactly they'll come by. So we can't just spend 8 hours a day out there waiting. When I take him out on walks he doesn't seem to care about any of it much since it's not by our house I assume. We've been taking him out on the leash in the yard alot lately but this isn't the sort of life we want for him. He does like to run around and I'd hate for him to be forever constrained to a leash or small kennel as our yard would cost thousands of dollars to fence. Especially because I can't take him on many walks right now since my car needs an expensive part replaced (so it won't be fixed for quite some time) and my mother is recovering from surgery so she can't really drive her car.

Does anyone have some advice? I'm just a teenager with no money but lots of time, and my parents don't have much time but are willing to spend a little if needed? Or do we have to consider surrendering him back to the shelter? Which I would hate to do as he's already attached to us and been through a couple homes (not for anything bad just fosters and a failed adopt cause he was too big) His breed is known to be stubborn and he definitely can be so we really don't know what to do.