They are usually strong in body and mind, educated and innovative, patient yet firm. If your farrier fits this description, hang on to him.
Scheduling is the most common problem in getting continuous farrier service.
My farrier has a slot for me in his schedule every six weeks. If I need services sooner, I can always negotiate for an emergency visit. If you have a great number of horses or if your horses differ greatly in their shoeing schedules, perhaps you could arrange to have your farrier come to your place on a particular morning each week unless otherwise notified. Mention any special problems that your horses may have so that your shoer can be sure to have custom supplies on hand when he visits. My shoers truck looks like a veritable store with its inventory of shoes, pads, nails and accessories all pigeonholed and categorized.