How do we keep our dogs away from a moderately busy rural road?

Hello dog folks! I need some fencing advice... My partner and I have 2 larger dogs and we live on 80 acres in a rural small town. A good chunk of our land is bordered by a 50 mph 2-lane road which makes us pretty nervous when it comes to letting the dogs off-leash. They're generally good about coming when called for and like to stay close to us while we do anything outside, but we would really like to let them spend more time out unsupervised. Any ideas on how we can fence our space so that the dogs may roam safely? Thanks!