Measure the height of your fence post to ensure you will cut the post off at the correct height. For example, if you are using 5-foot chain link fencing, cut your fence post at 62-inches. Leave two extra inches for your post end-cap.
Place a piece of tape around the fence post just below your measurement to mark your cutting location.
Have a second person hold the fence post securely. The post's in the ground but if you push on them you can disturb the fresh dirt around the posts and cause the post to move.
Cut around the top of the tape with an angle grinder equipped with a cutting wheel.