You need to make sure your dick is dead center in the middle. I often have to readjust several times after I start pumping to prevent the sides of the "accordian" from pinching my dick. I let the water out, and start over again. It is important NOT to use vaseline, as you don't want the pump moving around. It is best to keep your skin free of lubricants so it doesn't slide around. I got bruised a couple of times when I was starting out, but the bruises went away. Even so, I sometimes get accordian marks at the base of my dick, but I gently jelq after the session and they "iron out" and go away within minutes. Keep on pumping bro !