In this situation I would use what our training class refers to as puppy management. Take the dog and put him on a leash using a plain buckle collar. Step on the leash near the dog forcing the dog into a down position. Keep the leash very taught so the dog can not get back up as you continue to stand on it. It is very difficult for the dog to bark in this position.

Puppy management can be used for many different behaviors where the dog either jumps or barks when company arrives but is otherwise ok. This seems to be a little more owner controlled than the citronella collars (which I personally have seen others use but would not use myself). And since it is done on a flat buckle collar, it does not put undue punishment on the dog.