Massacre
The reason Ren Xiaosu's group chose this mountain path was because it had been gradually forgotten after the smugglers were rounded up.
However, this matter should be considered the other way around. You might want to take the most secretive path on the battlefield, but the enemy's infiltrating troops would also have the same thoughts.
Under normal circumstances, if an experienced military commander was present, they would tell Ren Xiaosu, "Don't be arrogant and try to take any secret paths."
That was because military troops would definitely be more precise than smugglers when it came to mapping out an area. If it were a path that was even known to smugglers, the enemy's troops would definitely know it as well.
No matter how decadent an army or dynasty was, one should not automatically assume them to be fools.