We recently had a situation where the party pinned an opponent and then used CMB to tie the person up. By our understanding, the person was then pinned by the rope. So they had two choices for getting out, escape artist and CMB. It was fairly easy to make the escape artist check high enough that an unskilled or moderately skilled individual couldn't get out. But with CMB checks, a natural 20 is always successful. So anyone can get out of rope bindings in 20 rounds (2 minutes). That doesn't seem right. I ruled that once you were tied up, you could only use escape artist, but I'm not sure that ruling is RAW. This should be clarified.