Questions for stopping my dog from stealing items.?

Only do it if its a tennis ball or something that is OKAY to be giving to you. If its something you don't want him to grab, make sure he knows not to grab that object again. Don't praise him when he's done something you don't want him to do in the future, that only shows him it's okay. Maybe you could hide some of these items as well if you can't do much about it? Hope this helped!