Q: I have a 3-year-old male shepherd mix named Joe. We have been going to dog parks and day care since he was a puppy, but now we have been kicked out due to his behavior. How can I train him to be nice at the dog park again?
A: Quite simply, you don't. I suspect that your dog has simply matured to the point of not wanting to socialize in the same manner as he once did, which is normal as well as expected. Let me put this into human terms for comparison:
When you're young, you meet up with other youngsters — at the park, on the playground, etc. Children chase each other and roughhouse, which builds strength and coordination. They play with toys, they learn to share, they practice actions that will be accepted by others, and learn to modify behavior that gets them into trouble. In short, child's play teaches life skills, in physical and emotional ways.
As adults, our style of play and interaction with others changes. Playground romps turn into family BBQs. You socialize with others you find enjoyable; you share stories. You learn how to seek out compatible friends at cocktail parties, and you'd likely be not only surprised but angry if someone tackled you like they did as a child during horseplay at the local park.
This same maturation process happens with dogs. Puppies go through a social period of development — learning how to play with one another, how to share, life lessons like "if I bite too hard, no one will play with me." As they mature, thoughts turn to more adult behaviors, some of which is influenced by inherited genetic traits. The sporting breeds will naturally want to look for and flush game; the herding breeds will want to chase and move others; the guarding breeds will become more serious and begin to guard. This is the natural course of maturation.
Of course, there are always exceptions. Some dogs do enjoy an extended period into adulthood where being social and playful with other dogs is still enjoyable. This most often occurs in the breeds that we have selectively bred to be mild mannered, like Labrador and golden retrievers, etc. But most dogs eventually outgrow the desire to have lots of social contact with other dogs.
It sounds like Joe has been telling you, perhaps for a while now, that being placed in an environment with other dogs of various ages and play skills is no longer his favorite thing. It's your job to interpret his behavior and "read" what he is saying.
Dogs that are not enjoying themselves among other dogs will often hang out at the perimeter, spend more time sniffing and investigating the environment, and may snap at or chase off others if they come too close or persist in instigating play. Your dog isn't behaving badly; he's simply trying to communicate.
Want to do the very best for your dog? "Listen" to what he is saying. Make more one-on-one time for him. Give him the exercise and attention he needs, from you. Teach him some tricks and play games with him to keep him mentally stimulated. Hire a neighbor or a dog walker to give him exercise and attention in a way he prefers.
And when it comes to day care or dog parks, remember that it's not about your wants or needs — it's about what is best for your dog.