If a dog snaps at you, that behavior must be stopped. Disciplining your dog doesn't consist of hitting him and yelling, though he must recognize a firm tone in your voice. Discipline consists of establishing firm boundaries and ensuring your dog recognizes them. He also must recognize that certain behaviors, such as snapping, are unacceptable.
Types of Aggression
Before disciplining the dog, you must figure out why the dog snapped. That's aggressive, unacceptable behavior, but there are different types of aggression. Dogs most commonly snap due to fear. Possessive aggression occurs when the dog thinks food, a toy or some other item or resting place will be taken away. Redirected aggression results when a dog bites at a person but really meant to sink his teeth into another dog. Dogs in pain might snap out of irritability or fear that a person will hurt them. The Merck Veterinary Manual website calls predatory aggression the worst type, because it comes out of the blue and often involves attacks on kids or babies, whose movements resemble those of prey species.
Snapping Versus Biting
If your dog snapped at you, he either didn't make contact with your skin or the contact was very light. As the American Society for the Prevention of Cruelty to Animals website points out, dogs have "wonderful control of their mouth," and if he meant to bite rather than snap that's what usually happens. Observe your dog and his behaviors carefully to head off problems. It's possible that he's been sending you signals that a situation is becoming intolerable, but you haven't noticed it. If your dog suddenly freezes and fixes you with a hard stare, that's a warning. Think about what might have triggered his snapping, so you know what sort of aggression you're dealing with. It also helps you prevent repetition of the incident.
Dogs are pack animals, who look to their leader for direction. It's imperative that are the leader of your pack, even if it consists of just you and Fido. Depending on the type of aggression the dog exhibits, it's possible that he doesn't respect you as the pack leader. That's especially true of possessive aggression. In this case, discipline your dog by taking away his toys. If he likes sleeping on the sofa and got snappy when asked to move, he's not allowed on it for the foreseeable future. As dog trainer Cesar Millan states on his website, "From this point on, [the dog] needs to live in your home on your terms, not his. You won’t be taking anything away from him; you’ll just be changing who’s in charge." Millan recommends removing any objects that trigger aggression so the dog learns that they only can be used when the pack leader permits it.
Disciplining your dog through counter conditioning involves using a lot of treats, preferably small ones. If you know what causes your dog to snap, you must desensitize him to these triggers and reward him when he reacts properly. It's not a short-term process. For example, if your dog snaps at you when you wear boots, he might be displaying fear aggression related to being stepped on. Desensitize him by leaving the boots out. If he approaches the boots, praise him and give him a treat. When he's fine with the unworn boots, put them on. Walk around with boots on, but do not interact with the dog. Get closer to him while wearing your boots, rewarding him and praising him as he approaches you without fear or aggression. Eventually, wearing boots becomes a nonissue.