The more you try to suppress more tense you will become. The best way to control( to have erection and not to have erection) is divert your mind to another useful activity. The best is do an abdominal breathing. Google it , learn it and practiced it regularly for 10 minutes twice a day. when you learn it, you can do the same when you have an sexual urge. With few breaths you will be calm and quiet. The more you use this technique, you become better at controlling your emotions.........Pratchett, practice and practice.