I was just playing some energy-burning, in-the-house, tennis-ball-throwing-down-the-hall with Foster, and I realized I was using very good tennis balls. (the $10 for 3 type) I just happened to have a lot of used penn and wilson balls left over from tennis and I just use those, I really like the bounce that they get. I find that dollar store tennis balls don't get more than 3 inches off the ground, and Foster really likes bouncy balls. This made me wonder, what type of tennis balls do you buy for your dog? Specific dog tennis balls, sport tennis balls, or dollar store balls?