Practice with "victims"
The person inside the box will be able to hear the dog but will not know if the dog is barking at the trainer or something else, and he or she will not know when to prolong or stop the signaling. Obviously all of this will depend on how the dog's humor and behavior is in that moment. This is one of the reasons radios are used. The person inside the box should not encourage or stimulate the dog verbally in the same moment he or she is indicated to, since this could coincide at the same time with a moment of silence, it should be done simultaneously with the next bark as this will help the dog to continue and will help it to associate and condition it. The next step will be for the person inside the box to remove the top and to continue praising the dog. Pat the dog and invite the dog to come closer so that it will begin to feel confident and comfortable to this "stranger" and to this new type of strange situation. At the point the trainer will then need to go up to the dog and praise and pat it too. The person inside the box will then need to get out of the box and along with the trainer praise the dog and have some play time. The helper will need to always reinforce verbal praise from inside the hiding place, avoiding this way any possibility of delay on the dog's part of barking from the moment the dog finds the "victim" and until the top of the box has been opened. The reason the trainer does not become involved at the moment the dog is searching for the "victim" is so that the dog will learn to firmly associate the person inside the box as a goal element. It will also help the dog to disassociate the trainer in this circumstance and will teach it to do the job on it's own.