The usual mode of protecting a well in the East was probably then, as now, by building round it a low circular wall.
Related Commentaries of Exodus 21:33
Exodus 21:33-34
33 And if a man shall open a pit, or if a man shall dig a pit, and not cover it, and an ox or an ass fall therein;
34 The owner of the pit shall make it good, and give money unto the owner of them; and the dead beast shall be his.