Parent who used to yell at your toddler...How did you stop?

We have 2 boys (4 and 18 months). 4yo is standard stuff. Lego focused, silly, some attitude and boundary testing which we are pretty good at dealing with positively. Talking about making good decisions and how we communicate as a family. 18 month is a whirling dervish. Hits, screams, throws, runs everywhere, physically endangers others and himself at a moment's notice. Climbs and jumps off furniture, tackles the cat, throws biblical tantrums. Only has a few words but is physically adept. Limited attention span but not concerned about aspergers or autism.Tricky part is that we are at the end of our rope. He is the hardest kid I've ever been around. It's a constant challenge to keep him from destroying the world. And lately, I've found myself raising my voice to get him to stop. Saying not only No or Stop but things like Why can't you sit still or just do something else. He's a kid. I get it and don't expect him to change at my speed.But I hate yelling at him. Makes me feel like a bad dad and definitely not the example I wanna set.So how did you stop?Edit: fixed words via /r/Parenting http://ift.tt/2Fpiuqv