Pierat,
I would think for the average dog, it might take a couple of months of training and some maturity on the dogs part. Along with practice...practice....practice. As well as exposure to tons of stuff. The exposure part, they suggest you start when the puppies have had all their shots. Take them everywhere.
It depends on the dog also. For my dog, the hardest part was to learn not to go "play" with the other dogs, but to stay focused on you. Some of that takes maturity. Most obedience classes help to teach your dog to stay focused. It took my first dog two obedience classes that were 8 weeks long, one day a week with lots of practice inbetween. The first set of classes was just basic; the second set was focused on helping the dog/owner learn the skills necessary to pass the CGC.
BTW, there were several older dogs in the classes as well.
Here is the website:
http://www.akc.org/events/cgc/index.cfm
I sure don't know how to answer the question about someone sticking their hand over the fence, then getting bit. That's similar to a situation we had at a boarding stable where we kept our horses. Horses will bite and one horse in particular was always biting someone. The owner wanted to put a sign near the horse to warn people not to put their hands in to pet him. The Boarding stable said no. Their insurance company had warned the barn owners that if they put a sign up about biting, then they knew/acknowledged the problem existed and should have moved the horse to a place where people couldn't get to him. Whereas if no sign existed, ignorance was claimed. Insurance is a tricky entity.
Having large standard poodles, both of them have been taught "four on the floor". I don't let them jump up on anyone. I had an older lady helping me with our horses when we had them on our property. I held my breath everytime the dog ran out to greet her. He could have "plowed" her down so fast.
Sorry for the rambling post. Animals are my love.
Propertylady57 how long did it take for your Roti to get his CGC?
Marsha~