The ṣ substitution does not take place in the s of the verb sedha when the meaning is that of moving.,
Thus अभिसेधयति गाः, परिसेधयति गाः ॥ This is an exception to 8.3.65.
Why do we say 'when meaning to drive'? Observe शिष्यमकार्यात्प्रतिषेधयति ॥ Here the sense is that of preventing or prohibiting.,