Your dog is instinctive and regularly acts on impulse. There's no need for your dog to be as protective over his squeaky toy as his wild ancestors were over their prey. Understanding the motivation behind Lucky's bad temper is the key to fixing the problem.
In the wild, intruders into a dog’s territory are seen as a threat to survival and are not afforded a warm welcome. In the domestic context, Lucky sees the mailman in the same way. This behavior is not appropriate, because visitors to the home do not pose a threat and are much more frequent. But that doesn’t take away Lucky's urge to protect his turf. Lucky may bark at, charge at or even attempt to bite a person or dog that he deems to be an intruder. You can help Lucky work on his manners by using a combination of desensitization and counter-conditioning. Together, these techniques gradually teach him to accept the presence of strangers and to form positive associations with them.
Dogs are pack animals and each pack has a hierarchy. There's a top dog in every pack and no two dogs are equal. In the pack, dogs learn manners and respect. Pack structure removes the need for dogs to squabble over access to food, access to mates and prime sleeping positions, everyone in the pack should know to wait their turn. However, to maintain this structure, ritualized aggression is necessary. Dominant dogs will growl at subordinates if they step out of line by, for example by trying to eat before it's their turn. In the domestic environment, Lucky and his pals will establish a pack order using the same technique. Problems typically only arise when well-meaning owners interfere with the pack order, for example by trying to give lowly dogs a social leg-up by showing them preference over their superiors. It’s better to monitor the dog behavior and only intervene if it seems like the aggression could result in injury, no matter how tempting it is to help out the bottom dog.
As with territory, resources in the wild such as food are jealously guarded. In a domestic environment, Lucky may get very grouchy if he thinks someone wants to steal his dinner. But Lucky has more things to be protective over compared to his wild ancestors, so he'll also pitch a fit if he thinks his toys, bed or even family members are under threat. He may growl or show his teeth to someone who attempts to remove his food bowl or put the toys away. To combat this problem, smart dog owners condition their dogs so they learn to share. You can achieve this by regularly moving and handling items such as food bowls and toys when Lucky is young and by rewarding him for remaining passive.
Fear is a survival instinct that all dogs have, although some are more prone to feeling it than others. When Lucky is spooked, he shows this through his behavior and body language. Cowering, avoiding eye contact, hunching and licking the lips are all signs that a dog is scared. If a human or another dog ignores these signs, the fearful dog may feel his only option is to be aggressive. Understanding canine body language is key to preventing fear-aggression. By knowing when Lucky is scared, you can remove him from the situation before it turns ugly.