We have 2 acres with a radio fence, the boundary wire is just that yellow bell wire, and in some places it's visible on the ground. Took the dog to nephew's soccer game 2 weeks ago, and they had that cheap yellow propylene rope strung up as guides for parking etc. As we walked toward the field, the dog dug in like a mule and refused to budge. Would go in any other direction besides towards the rope. I finally figured out that she associated the rope with teh boundary wire.
My uncle used to camp with dogs, and he would just bring the training flags instead of the whole system, said the dog knew what they were and didn't go near them.
That said, a leash is your best bet. We use a 20' cotton training lead tied to a tree or the RV steps, enough to let the dog wander around the campsite, but short enough to keep her in the campsite.