Are you using a string loop as well? You can keep the peep aligned by using one...usually.

Whenever someone states that the peep is rotating, it is usually caused by a couple of things. One, the string isn't very good to begin with. A good set of strings will not have peep rotation issues. Some manufacturers use very good strings on their bows, others use very bad strings. I won't mention names. Another reason a peep will rotate is if the string is very old.

Generally peep rotation issues are caused by the string creeping or stretching over time. You can have it set perfectly one day and the next, it will be completely off. A high quality string will not have these issues.