I used to use a rubber patch to straighten my leader until one day I noticed the leader had visible damage from doing this. I didn't have any real feel while using the rubber patch and pretty much burned my leader by applying too much pressure while trying to straighten it. Since then I have been using my two best tools for straightening leaders, my hands. I simply put the leader between my two middle fingers and the base of my palm, squeeze a little bit, pull the leader and I'm done. It will burn a slight bit, but I found that I have good feel and can adjust the tension as needed.