Get your ferrets hand tame first mate, handle them every day after they have been fed, Talk to them so they learn your voice because their eyesight is not so good they dont know whats trying to pick them up.
I have my ferret hutch near my kennel so the dogs see the ferrets daily and eventually pretty much ignore them, gently introduce them to your dog, don't just let them all out together....
Hold the ferret and let the dog sniff it, if the dogs the timid type and sharp "no" should give him the idea, if not a water pistol works well.
Then let the ferret run loose but hold the dog (waterpist