גְּֽבוּל־שַׂ֭מְתָּ בַּל־יַֽעֲבֹר֑וּן בַּל־יְ֝שׁוּב֗וּן לְכַסּ֥וֹת הָאָֽרֶץ׃
Naglagay Ka ng hangganan na hindi nila malalampasan, upang hindi na sila bumalik para takpan ang daigdig.
Rashi
You set a boundary for them, viz. the sand that is around its shore.