A sharp X-acto knife works perfectly. Use the very tip of the blade, and do not allow any of the hairs to get "pulled" while you are cutting.
In other words, if there is no "tension" on any of the hairs, there is much less risk of cutting them accidentally. With scissors you always run the risk of cutting the hair along with the base. Anything that is trapped between the jaws of the scissors will get cut. A knife blade is much more forgiving.
I even used a knife to trim the excess base material off another hair wearer's piece WHILE IT WAS ATTACHED TO HIS HEAD.
This is by far the safest method of trimming the base. Eventually I will have this method on video. Stay tuned....
