Hi Charles. This is par for the course for outbound. My advice is:
1)Try building in incentives and goals that make reps stay for a least 9 months-it could be something like offering a certification over that period or moving to a higher level if they stay for that period.
2)Also look at the age of your reps and I am sure you will find that most of them are under 25 yrs. Try to get older, more mature reps and they will provide stability and are less likely to move around.
3) Attracting the right mix of people is the ultimate challenge.