-On the verse by Yackov it says "He placed a rock under his head".
-The Midrash says this was to protect him from wild animals.
-A rock under the head would not keep away wild animals. Rather it is referring to Lilim which are referd to as 'wild animals'.
-Yackov never saw Keri in his life and this is one of the tricks he used, he would always place a rock under his head as he slept.
-The Ari writes that it is a big Tikun to do this. It greatly helps to prevent Keri and keep away Lilim.

-Place the rock under your head and do the following Kavanah before you go to sleep.

One can wrap the rock in a pillow case if he wants.
-Also if one does not have a rock he should visualize that there is a rock and he should do the Kavanot.