To have a successful referral system you need to incorporate several things.
1) Every referral system you have needs to be documented. This allows you to track and see how many referrals you are getting from each referral system.
2) Every referral system you have also needs to have a key component in each part of the document. The question/part is this: What can be improved? What needs to be modified? This way the system fixes itself and improves automatically over time, because it has a feedback system.
If you implement these into your referral systems you will be extremely successful because you will get referrals and then tweak and modify what does and does not work.