I made this ball for a friend's dog, Charlie.
They are very easy to make. I used a skein of Deb Stoller Full O Sheep yarn, but any 100% wool will work, including unravelled sweaters. For a lighter ball you can start to wrap around a base of wool scraps or batt, but I wanted a heavy, sturdy ball so I just wound the skein into a tight ball. Tuck in the loose end and put the ball inside an old knee high or old fashioned panty hose, tie a knot so the ball is firmly wrapped, and throw it in the washer with your laundry. I set it on hot wash/cold rinse and just leave it in through several washings. When the wool fuzz shows on the outside of the knee high it's ready. At that point, move it to the dryer for a few cycles until it's dry. If you want to personalize it, take a foot or so of contrasting yarn and needle felt the name (or design) firmly onto the ball. I put it back in the knee high and repeated the washing/drying a few more cycles to make sure it was firmly felted. Make sure it's dry and you're done! These balls are quite sturdy (unless your dog likes to chew up balls, mine just wants to play fetch so these are great for that). They also don't get as slimy and soggy as tennis balls, so they are more fun for the humans. Plus, they look cute and are washable! If they get ratty you can refelt them with the knee high/washer method and they are as good as new.