I used this
Stewart® Pro-Treat® Beef Liver Treats for Dogs - Treats & Rawhide - Dog - PetSmart during a trick training class, and Joey really loved it. It was the only store bought treat he loved week after week. I bought many things he lost interest in after a while. However, it's very expensive, and I thought overpriced. You can buy beef liver very cheap, about 1-2 dollars a pound. Most grocers have them in their freezer. If you boil it 30 minutes and cut it into one inch squares and bake in 250 over for a few hours until it seems dry, you get a lot of treats for your money. I kept the treats in the freezer and just kept a week’s supply in the fridge. They are nice because you can keep them on you in a bag and they don't spoil if left out all day. Joey absolutely loved them. If you prefer buying some, buy beef liver not chicken liver.