perimeter training

Question
We have a 4 month Shetland Sheepdog who I would like to train not to go out into a very busy road. As he is smart and knows several commands now, I would hope to be able to train him without getting an invisible fence. We have about 16 acres, only about 300 feet of road frontage. The rest is river and stone wall.  I have trained an earlier Sheltie to CD level.  When the earlier Shelties moved with us to this home, we had no road problems.  Thank you for any help you can give me.
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Answer
I'm not a big fan of invisible fences (they don't keep anything else out, and sometimes they don't keep the dogs in - if the dog gets excited and accidently goes through, then it cannot come back through without receiving another shock. And they can malfunction and really traumatize a dog - especially a breed as sensitive as a Sheltie. However, I also would not recommend what you are wanting to do - especially with a busy road. No training is 100%. You may get lucky, and nothing ever happens to entice your dog into the street, but there are always a few percentage points worth of uncertainty there. Additionally, larger dogs and wildlife are not deterred from coming into your yard and injuring your dog if he's outside unattended. I would take the money you would otherwise spend on an invisible fence, and fence him an exercise yard with physical fencing. And let him be loose on the property only under your supervision, after he has learned a really good recall.