• Do sit stays on a soft, comfortable couch or bed.
• Have your dog do a sit stay while playing fetch with another dog.
• Teach your dog to release on a verbal "Okay" signal only. Do not let your dog release on just a hand signal. It is too easy for them to back-chain, and start releasing themselves on the physical signal that precedes your hand signal, for example, a turn of your head.
• Practice fooling your dog with a similar verbal release word, such as "Ohio." If he breaks, put him back in a sit, without saying anything. Once he is reliable with this, practice doing both a fake release word, like "Ohio," along with a hand signal at the same time.
• Attach a 6 foot leash to your dog's buckle collar. Tell your dog to stay, and walk to the end of the leash. Apply pressure to the leash, forcing the dog to brace himself to stay. Release you dog towards you. Once your dog is successful with this, do the same exercise with a much longer leash, so you can have a longer "lead out."
• Do the above exercise right before you go in the ring, or right after you exit the ring. That way they might be revved up, like they would be in the ring.
• Experiment with starting from a sit or a down at the start line. See if your dog is better at one than the other. Whichever position you choose, the dog should not move until you release him.
• Consider pulling your dog off course if they break the start line before you release them. If the dog's reward is doing agility, then it doesn't get its reward if it breaks the start line. If you do this, you must be consistent and do it every time, or else you are only confusing your dog. Matches are a less expensive way to train this than trials.
• When you leave your dog at the start line, walk confidently away from them. Do not "tip toe" out, hoping your dog won't break - it'll probably just excite your dog more.
• I have found that sternly yelling "stay" at my dog does not work. It only makes him that more excited.