The best training tool I believe is a natural shed. Why not train with the real thing? The first day I got my pup I gave him a fresh shed. From then on, his toys consisted of fresh and OLD bone. We played fetch in the house, hid horns in the bathroom, under the bed, behind doors. We did this same game outside but expanded it. Its not all about them using their nose to find you horn, u want to train them to spot them also. Old white sheds work great. I know I'm no dog expert, this is my first dog, but he sure knows what he is doing in the woods.
