Nikko practically jumps out of his skin with excitement when he sees his harness but he squirms so much that I can barely get it on. what works for me is that if he wiggles too much I tell him "forget it, no outside Nikko!" and make a show of putting his harness down. He actually whimpers when he thinks I'm not taking him outside and calms down enough to allow me to put it on him. Clothes are a different story. Its a total wrestling match but once the sweater or coat is on he forgets about it.
