At all these times every precaution was taken to prevent any one getting out surreptitiously.
This narrowed down the possibilities of passing the limits of the pen alive, to tunneling.

This was also surrounded by almost insuperable difficulties.

First, it required not less than fifty feet of subterranean excavation to get out, which was an enormous work with our limited means.

Then the logs forming the Stockade were set in the ground to a depth of five feet, and the tunnel had to go down beneath them.
They had an unpleasant habit of dropping down into the burrow under them.
It added much to the discouragements of tunneling to think of one of these massive timbers dropping upon a fellow as he worked his mole-like way under it, and either crushing him to death outright, or pinning him there to die of suffocation or hunger.
In one instance, in a tunnel near me, but in which I was not interested, the log slipped down after the digger had got out beyond it.
He immediately began digging for the surface, for life, and was fortunately able to break through before he suffocated.

He got his head above the ground, and then fainted.