My experience - doesn't matter what type of leash/collar you use - if the dog is not trained, it will pull on any and every leash/collar.
If he can't find a full-fledged training, then he should talk to some local knowledgeable dog folks and see if one would give him some one on one assistance.
1975 American Clipper RV with Dodge 360 (photo in profile)
1998 American Clipper Fold n Roll Folding Trailer
Both born in Morgan Hill, CA to Irv Perch (Daddy of the Aristocrat trailers)