Scince we live aboard our boat in summer, I had an idea. I've been taking him out in the tender far enough from shore that swimming to land isn't an option. He goes in after his ball & has no choice but to swim back to the inflatable. He has to give up his "prey" to me in order to get back in.
Now I can do it from shore and he comes back to the tender & gives it up. Of course, can't do this with a gun, but he's coming along.
Only the ignorant find ignorance to be bliss. Only those of us who know better will suffer from it.