What is the meaning of "Al Ta'amod Al ha'Perek"?
Rashi: Do not stand at the junction where fleers leave. Radak - Edomim stood there to prevent Yisraelim from fleeing.
Hagahah (in Rashi, from R. Ovadyah ha'Navi): Do not interrupt between the paragraphs of Keri'as Shma.
Why does it add "v'Al Tasger Seridav"?
Malbim: (a) (Do not stand at the crossroad to prevent Yisraelim from fleeing.) And at least, fugitives who escaped to your land, do not return them - "Lo Sasgir Eved El Adonav Asher Yinatzel Elecha me'Im Adonav" (Devarim 23:16). (b) The verse hints to what Edom did after the Churban. First they saw the evil of Yisrael and prosecuted against them. After the Edomim got stronger and their creed spread, they began to constantly despoil Yisrael's wealth. Afterwards they began to cut off the refugees via decrees, expulsions and Hashmados (decrees against guarding Mitzvos), and later they killed the ravished survivors and handed them over to the governor, judgment and harsh afflictions.
