I have only used a dog on one occasion to trail a wounded deer. I shot a small buck who quickly headed over the hill. I heard him fall, so I expected an easy retrieve. Unfortunately there was little blood, and, no he was not easily located.
I went to my friend's house, on whose property I was hunting, and asked if his Lab might find him. We put Buck on the scent but he seemed to only circle back to the creek, exactly the opposite direction the deer ran. We called him back a couple of times, cursing him severely, and put him back on the scent. Finally, we went to get him and put him on the leash to take him home. He was standing on top of the deer. I owed that dog many apologies for the things I had said. It is very doubtful that I would have recovered the deer in the dark without Buck.
After reading Jerry's post it is clear that I made several mistakes regarding the manner I handled the scene before putting the dog on the trail. I was lucky. The advice he gives makes a lot of sense, and I will sure keep it in mind if I find myself needing to get the assistance of a dog again.