Funny, we tried to get Bulz to do that with the foam buffalo targets at the Evergreen Bowfishing Booth.

He commented something about our shooting skill and declined. (he seemed more worried about us than the newbies trying out the bows)

The problem with the foambuffalo is that it floats (much like a big piece of foam... go figure ) I like using plastic water bottles. You can let water into them and then they'll sink a bit. You can tie them off to a weight so they can't escape.

At Evergreen we used motorized swimming fish in the stock tank. Those were really cool, but they won't survive a real fish arrow.