Use a long line or flexi with a fixed collar for this exercise. Give your dog the command ‘stay’ and show a toy or a candy. Go back about 20 meters and drag your feet over the ground to leave as much odor as possible. As you do this you keep the reward close to the ground to let the dog search on the ground. Place the reward at the end of the track and then return via the same route. Then give your dog the command “search” for the candy or” find “for the toy, encourage your dog to sniff on the trail you have walked, until he finds the reward, to make the exercise gradually more difficult you can make the track longer, walk in different directions or run according to different patterns.