What is a "Gader"?
Rashi: "Gader" is 'a stone wall'.
Targum Yonasan): It refers to the pile of stones and the monument that Ya'akov and Lavan erected
with an agreement
never to pass them in order to do harm to the other.
Which explains why it caused Bil'am to become lame. Refer to 22:25:1:1.
See end of Vayeitzei.