I think the electric fence is a great idea, if you are worried about people feeding your horse. As for being safe yourself, I don't think you have much to worry about. Truckers are just making a living like anyone else, they are not on the hunt for vulnerable girls. Many of them have daughters just like you. If you respect their space, they will respect yours. I am sure if you stay in your riding areas, you will be fine.
And *please* don't go knocking on random doors. I can't think of a worse idea. Especially if you are concerned about personal safety, marching around asking strangers if you can put a horse in their backyard is not your wisest course of action. If you live in a rural area that is anywhere like mine, you might have paranoid old rednecks that sit behind their doors with shotguns waiting for tressperserz.
The basest horn of his hoof is more musical than the pipe of Hermes.
He's of the color of the nutmeg and of the heart of the ginger.
His neigh is like the bidding of a monarch,
And his countenance enforces homage.
- William Shakespeare