While I am not a huge fan of the practice in JH, sometimes judges will use a duck call to signal the gunners. It is therefore good to practice having someone call behind you and your dog before the mark is thrown. This prevents a scenario where a dog spins around and stares at the judges and doesn't get turned back around to see the marks fall. If you practice this a few times, the dog usually quickly learns to ignore the call behind it.
Lastly and most important, practice having someone behind you call your number (just make one up) after the mark has fallen. This will hopefully prevent you from releasing the dog prior to the judges giving you the OK to do so, which can make for a short day. Many moons ago when I ran my first HT, I counted, "1001, 1002, 1003" after seeing the bird fall and released my dog, as I had done hundreds of times in training. Moments later, I heard, "dog #7". Dog picked up the chicken and we both went home. Bummer.