I have seen a lot of commentary about yellowjacket issues and wanted to offer my experience. After our bees absconded in the fall our first year (likely due to yellowjackets), I did some research and found that yellowjackets are dumb (as are honey robbers) and can easily be dissuaded by something covering the front of the hive. I cut up an old bedsheet and have it tented over the front of my hives (see pictures) and this has kept yellowjackets out. Interestingly enough, I did an experiment of sorts this year and left my super strong aggressive hive untented and initially tented only my weak hive. Within a few weeks, the strong hive was mostly gone (no dead bees, just gone) and the weak hive was still thriving. Yellowjackets are TERRIBLE in my area - when I got in my hives last week during the sunny period, I was literally killing yellowjackets in the air with my hands. As soon as I open a hive they show up. (I've been able to frankenstein together a new colony with a friend's extra small colony and some extra brood from my other hive, fingers crossed they make it through the winter.)
This is a super simple and effective way that I've been able to keep yellowjackets from pestering my hives. Hope it helps someone else!
(the clear corrugate shelter is our winter experiment to see how it helps the colony survive the wet and windy winter)