My puppy is 3 months now. Up to a week ago he would bring the bumper back everytime.I was working him four or five times a day, but only for a max of five retreives. This last week I back off to only a couple times a day. I thought I may be pushing him to much. Now he is laying down with the bumper and will not bring it back or he tries to go around me. Should I use the rope on him and make him come to me or should I wait till he is older. I do not want him to get a habit that will be hard to break him of. Retired.