It’s important to practice recalls frequently, and make them rewarding. Too often, we call our dogs for not-fun things (baths, nail trims, to end playtime). These can discourage responding to recalls in the future.
For practicing distance recalls in open areas, use a long line or a confederate, as in this video. Be sure not to go too far and scare your dog, especially if using a long line.
Since Sirius Black is blind, constant verbal reinforcement keeps him moving in the correct direction.