I have an 11 month old Collie/Aussie mix who is a little scared at the dog park around other dogs and he growls a bit and runs away. He is fine with my other dog though. Any suggestions?
A dog park might be a little too much for your dog right now. Too many more eager and/or aggressive dogs. When your dog growls, he's just telling the other dog to back off and leave him alone. However, there's inevitably another dog who continues to ignore the message and will keep trying to play with your dog, and the situation can escalate. Start him off slowly with other dogs. If you have friends or neighbors with dogs, invite one over for a playdate and then introduce him to others, gradually increasing the number. Also, you might want to look into facilities that have not daycare, but playtime, for dogs according to size. There's a facility near me that has Saturday morning playtime for a nominal charge (I think it is $5) for an hour and the dogs are all in the same weight range, but that may not be so much of a concern for your medium-size dog.
As Karen suggested, go slow, introducing your dogs to known, friendly dogs, giving him treats and encouragement for showing brave, social behavior. Work your way up to multiple dogs. Take him somewhere near an area with a lot of dogs passing through, like a park or a popular walking street, and reward him for being relaxed. Gradually work your way closer, so he may safely come into contact with some friendly dogs. He may never be a dog park dog, but that's ok. Dog parks can be great if you have a very well adjusted, easy going dog, but for dogs with anxiety or fear issues, they can be very dangerous. A lot of owners have no idea how to read their dog's body language, and many people see dog parks as a place to get exercise for their high energy dogs after they've been cooped up all day. A bunch of high energy, overexcited dogs in an enclosed space usually spells trouble. Many dogs (even if they are friendly generally) will gang up on a single dog showing signs of fear, and a fearful dog may learn the only way to feel safe is to react with aggression. If your dog does improve with his anxiety and you still want to use the dog park, I'd recommend identifying dogs who are good matches for your dog and getting to know their owners and arranging to meet them there at off peak hours to avoid the busiest, craziest, scariest times, and always listen to what your dog is telling you. If he's uncomfortable, be his advocate. Move him somewhere in the park where he feels safer, or leave entirely.