Traditional harnesses (where the leash is attached to the back of the dog) are allowed, but for some dogs they can make it more difficult to teach polite leash walking. Training at J9's K9s is typically done on regular buckle collars or for strong leash-pullers, harnesses like the Freedom No Pull, Balance or PetSafe 3 In 1 which also have a place to attach the leash on the front of your dog's chest in case he's an exuberant walker.
Choke chains, pinch/prong collars and shock collars represent “old fashioned” compulsory training methods designed to teach the dog to obey only from fear of being hurt. These methods are at best, damaging to the relationship between you and your dog. At worst, they can cause permanent physical and/or psychological damage. These collars are not allowed at J9's K9s.