My dog has lot of toys, but the only ones he wants to play with outside are footballs not even dog toys. Inside he sometimes wants to play with other toys, but he barks if we pick it up and throw it. If we have a football he will go crazy and jump on us to grab it. Outside he will do the same, he will hold the ball in his mouth the whole time while running. And if we get close he will bark and jump on us. He has never bitten us and im not afraid of that, cause hes a sweet dog other than that. He is 4 years old and a border collie mix, how can i teach him to like toys like tennis balls and teach him to fetch it? He has other behavioral problems and im considering getting a trainer to help me.