Actually, I was wrong when I said these were "rainbird" heads, they're actually "MP3000" rotor heads. Turns out they can't be turned off altogether...only the arc and the radius can be adjusted. Looks like I'll just need to replace this particular head if I want to be able to turn it off...

Well, DH figured it out and we are not watering the driveway anymore. Took a bit of patience, go figure!

Has the problem sprinkler head worked properly before? I'm no expert, but here's what I could think of as being the problem (in order from easist to hardest to investigate and fix). 1. The head needs adjusting. Go to the manufacturer's website and find the instructions on how to adjust your model of sprinkler head. They usually have an e-mail address where you can ask questions if you don't find the answer. 2. The head is clogged or broken. Flushing the system usually prevents clogging, but it can still happen. Where I live, the city replaced the water meters. In so doing, they introduce all kinds of muck into the water supply. I also had an earwig crawl inside one of my fixtures and clog it up. They seem to like water. You could try swapping the head with one of your other ones or with a new one. This means digging. If you swap, and the other one works fine but the problem one is still "pissing" in its new position, then you probably have a bad head. 3. There's a clog in your pipe, or the pipe is broken. I'd look along the ground where the pipe runs to see if you notice any wet spots. You could dig up the head, remove the head, flush the pipe. Let's hope it isn't #3.

You can flush the head by removing the nozzle and turning the zone on for a few seconds. If water comes shooting out, then the blockage is either gone or was never the problem. Also, check the filter under the nozzle for debris.