Yes. If you were black and walking around without a chaperone in the South, you either had to be a free man known to the community or needed a paper from the slave owner letting people know the slave was trusted and allowed for that particular trip. Some owners would let their slaves go on dates to neighboring plantations. My guess as to why they didn't run away more often is that they were either, like you said, treated very harshly, or they accepted what they were born into. Reading and writing was usually not permitted, so that kept their communications and options to a minimum. Also, some slaves were treated somewhat like family. Well, family that was forced to stay on the plantation. It also seems like the farther south you were, the harsher the slaves were treated and the harder it would have been to escape through slave territory into the free North.