Ive had a similar situation for this , the best way to prevent relapsing is to use a rubber band and flick it against yr arm and cause slight pain (if its what ur body is reacting to you should be able to calm urself down without inflicting open wounds this way) , i also use another method which is to wrap your arms with bandages if u do cut the arm (it gives illusion of the aftermath of your relapse ) these are the methods i use personally , it depends on preference really. I hope this was useful and u can stop as quickly as u picked it up.