We were having a grand time with this toy, and my dog enjoyed running the extra distance.  That was until I handed it over to my boyfriend who "Chucked it" as hard as he could and our tennis ball was lost forever... Ok, so that's not really a problem since you can put whatever kind of tennis ball you want in there, but buyer beware: You must understand physics to avoid losing your dog's favorite tennis ball or possibly chucking a ball into a passing car.  It really depends on where you live.