I'm pretty lax defending wheels for the most part but if I do want to hold it I try to make sure my bars are in front of the other rider. For the most part if it comes down to a situation where a guy is fighting for my wheel and we do several bumps or taps I'll probably cede the spot. Its just not worth it. Also, I think you have to be in a good spot with your bike handling to do that. 2 years ago maybe, but rarely riding in packs in the past few years, not today.
For the most part I'm just opportunistic on wheels, I don't force my way in but if I had any talent in this sport its knowing when someone is going to jump. Maybe its obvious to the experienced guys here as well but not many racers in the 4's. Also I find having a good variable cadence really helps because jumping up to 120 for a few seconds closes gaps much faster than shifting.