My toddler (17 months old) has not responded to various "discipline" methods that we've tried. Basically, if he does something dangerous or he shouldn't do, such as climb on top of the coffee table, we try to convey that it is inappropriate. We've tried telling him no, explaining that it is dangerous in a stern voice, and even time out in the corner. He just laughs and thinks it is funny. What can we do to help him understand? Thanks!