I finally got off my butt and made a water ball yesterday. It was surprisingly easy using an attachment from the air mattress air pump. I had been planning on attaching it to a milk jug to create a funnel and slowly fill the ball up, but sense prevailed and I just duct taped it right to the end of the hose and cranked that sucker up. 10 minutes later I had my water ball. As you can see I started to fill the ball up nice and slow, but then realized how long that would take.
I've just carried it around a little bit as a finisher to my max strength workout last night. It's extremely effective for grip work, grabbing the folds of plastic in your hands and trying to hold on. I did a little of that, but I also just wrapped my arms around it and hugged it close. I'm going to be working that one a lot. On Monday we were practicing take downs from behind and in the middle of it my arms just gave out. I had the strength to keep moving, but my arms were just too fatigued to keep my grip around my sparring partner's waist. The water ball is the only thing I've tried that has come close to being a good simulation of that. Now, getting an empty keg is next on the list.