I use "no" when needed. DS now uses "no" - he starts to empty the kitchen cupboards and I hear this "noonoonoonoonoo" noise! He knows it's naughty but he doesn't have the self-control not to do it. Same as going behind the TV. We have very few "no" times at home, but I don't baby proof the home. I usually try "Liebling, do good boys hit the TV? Are you a good boy? Do you hit the TV? Would you like to come and use the hammer on the toy here?" I wait for him to say no, yes, no, yes - and the toy is one usually one you can use a hammer on, like a xylophone or a shape-sorter with hammer. I let him decide what is acceptable behaviour (after telling him a few times previously) and he's pretty good with it - but then, he knows he's a good boy!

The only time I have to shout "NO!" and stop him right away rather than let him stop himself or distract him is usually by a road or if he is going to attack another child. But after I've stopped him I'll still go through the "Is it good boy to hit? Are you good boy?" routine.

Each child is different and this may not work, but letting DS set his own rules (which I have already set for him) works wonders and it will help when he's older and establishing his own boundaries when I'm not there.