No. While it is extremely unlikely for a greyhound to get courageous enough to hop a fence, they are large dogs and are very agile. Jumping over a four foot fence would be extremely easy for them, a 5 foot fence would be about perfect.
Setting up a 4-foot fence to restrain an Italian Greyhound wouldn't be a good idea. These dogs can actually scale a six foot fence if motivated. A fence with a height of between 5 and 6 feet would be perfect.