Hi I have a 5 months old puppy and she won't play fetch or drop it. She will chase it and bring it back but she won't drop it. She knows what drop it means but she won't do it, she will only drop it and play fetch if I have ham treats. I have tried everything from having two balls and trading it, trading for treats, running away from her when she brings it back, enthusiastic encouragement and plenty of other things that don't work. Need some help please!