I would recommend both the Madd Dog and ACSM certification. I have both and they are highly respected. Be sure to check out the information on Continuing education credits. The CEC's can be costly.
Thanks! It helps knowing that I'm doing all this work for something good. I know the continuing education requirements are expensive. Hopefully, though, they have substance that I can pass along to my (future) clients.
To train a dog, you must be more interesting than dirt.