That's an enviable result!
It's not a particularly huge area I'm trying to keep them away from (similar to your 30' long one story deck), so I'm pretty confident in asserting there aren't any weeds touching the wires. And the wires are well-insulated with plastic separators intended for the purpose.
I only have the one ground rod, and maybe that's insufficient (though like I said, it seriously zaps me if I'm not wearing shoes -- as in, the thought of maintaining contact for more than an instant is laughable). I've read elsewhere now that the makeup of chickens (light bodies, weird legs, feathers possibly) might make them a little more resilient than (for instance) most mammals. But I'm heartened by your success story.
The biggest weakness of my setup is probably that I currently only have one wire for most of the perimeter. It seemed like that ought to be sufficient to discourage them once they'd bumped against it and been zapped. But though they definitely come into contact with the wire, at least one of them just slips on under my 6-inch wire all casual-like, without any apparent discomfort.
I'll add one or two more wires, and maybe make the middle wire a ground wire. Are your three wires spaced out evenly over the 2 feet? So the top wire's at 24 inches, and the others are at like 8 and 16ish? Seems like they might sneak under the bottom wire at 8 inches.
Hope all the questions aren't too annoying, I'm just extremely eager to duplicate your success and finally claim back my patio for human use! And I don't want to fence the patio in as though WE were the cooped ones (and I really like letting the chickens roam around the yard instead of only having a little run).