"Runaway Slaves: Rebels on the Plantation" by John Hope Franklin and Loren Schweninger;states...

"Because runaways were seldom advertised unless they had been gone as much as a month, the total can never be known. The authors estimate that they may have averaged fifty thousand a year or more. The number advertised from 1790 to 1860 was only about 8,400, but the authors argue that "while runaways constituted a small minority of the slave population, they were of enormous significance in the plantation universe" Edmund S. Morgan.

Why did they runaway and fail so many times? Because they were not running away for ever. They hardly ran further than a couple of miles, and most often came back on their own. This social action was the slave's way of controlling the master. When the slave wanted change in his life he ran away to punish the master. He would even take a whipping to do so, but in the end, the master, in order not to lose money, would give in. Most of the complants were about work, or social gatherings, or even finding mates.

Slaves were known for knowing the best techniques for hiding. They were rarely caught.
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David Upton