How do I get my golden to stay calm around other dogs?

My golden retriever is coming up for two years of age and is fantastically well behaved following all commands on a one to one basis. Unfortunately when we take him to the park or out for a walk, he will run away to play with another dog ignoring the 'Olly here' command or get extremely excited and pull on his lead if he is near one. He seems to forget that he is not supposed to jump all over the other dog! Any suggestions would be welcomed.