Your dog goes through three general phases of learning:
1. "The Learning phase": This is when the dog learns to understand what a command means. You use very little correction at this phase, and may use toys, balls or food to motivate (not bribe!) the dog into doing and understanding what the command means. The problem with most amateur dog trainers is that they feel their dog is trained, once he understands a command and has gone through the "Learning Phase."
2. "The Reinforcement phase": Once the dog has learned what the command means, he needs to be "re- taught" the command in a variety of different settings. Because he'll likely only associate response to the command in the initial setting you've trained him in, he needs to "relearn" the command in different types of areas. This happens very quickly. It usually only takes one or two repetitions, and then it "clicks" for the dog. Once you see that it's "clicked for the dog," this is when you need to start working very fast, exciting and BRIEF sessions. Your goal is to get the dog to respond to commands very quickly. IF you're working on the "down" command, then the dog should drop into the down position very quickly--AND THEN IMMEDIATELY GIVE HIM YOUR "RELEASE COMMAND!" Run 5 or 10 steps with the dog, then reissue the command. When you give him the release command, toss a ball, or a piece of food. You should be aiming to teach the dog that training is a big, fun game. A game that he has to respect. But nonetheless, a game the he loves and looks forward to playing with you--in any environment.
Here's where most new trainers fail: They don't work the dog fast enough. You need to make your body language fast and exciting to the dog. IF you're not sweating and huffing and puffing after 5-10 minutes