Agree with the other posts, short practices. Make sure they understand whoa. I use 2 leads, leave a heavier one down & use a lighter one (even a piece of twine) so if they try to move away I can make them get right back where they need to be. It's amazing how quickly they learn to stay put, especially if "whoa" was already there. Like Little Ones said, once they're good in one place, take them to another. You can even increase activity around them (I'm mean, I put their feed pan out) and see how well they do. Be creative, be consistent in your methods, and add variety to what you're doing.