I am going to be putting in a high tension electric fence for horses. I am going to use 6 inch wooden posts for the corners and 4 inch wooden posts for the line posts. I live in an area that gets very cold and the frost line is 4 to 5 feet deep. The fence manufacturer recommends that posts should be below the frost line. If I put the posts down 5 feet and cement them in, wont the frost push the post up by pushing up on the cement ball around the post since most likely the cement ball will not be below the frost line. If I do not cement the post in will it be secure enough?