No bargaining or bribes. Don't be a negotiator, be a benevolent dictator. Make him suffer in ways that are not cruel, but are important in his world. For instance, my daughter sprayed sunscreen in her own face after I told her not to touch it. Now, she doesn't get any TV for the whole weekend. And I plan to stick by it, even if she tries to talk or whine her way out of it.

Other punishments that work are taking away her favorite toy, taking away dessert while everyone else eats it, and making her go to bed early.
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http://www.altparenting.com

Not meant to be a plug for the book (which you can might find at your library), but here are some more extensive tips on discipline:

www.loveandlogic.com/pages/aggressivetoddlers.html

I don't assume that your son is "aggressive" - I focused more on the age rather than behavior in your post. We use some of the Love and Logic stuff but I guess my booming voice keeps my kids tamped down pretty well. They don't like to hear dad's bark.

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Gettin' creative at CreativeDad.net