If this were my dilemma, I'd yank that big rosemary out and replace with new plants. You will be able to keep the new plants sheared on a regular basis so that you'll always have lots of juvenile (rather than old) wood. Rosemary can be clipped back to an attractive hedge like appearance a couple times a year. The heavier (older) growth will be kept very close to the trunk this way.

I can only dream of having such a dilemma!

Rhizo_1's got a point, though...I think it's easier to keep bushes in check from the beginning rather than to bring them back when they've gone too far. However, I understand that some people have had great luck with cutting rosemary all the way back and letting it re-grow.

Rosemary will take pretty hard cutting back. You could saw back half this year and half next if you are concerned about overdoing it. And meanwhile take cuttings. My rosemary is getting on for 20 years old so I'd be loath to destroy it. I just give it a good trim.

Thanks for the replies! I'm leaning toward yanking out the monsters and starting over, but I may start with cuttings now so when I've steeled myself to "do the deed" I can have the monster's children.

If you're willing to leave your current rosemary in the ground a bit longer, you could try to make babies by layering rather than by cuttings. I find that approach pretty easy. I do it by cutting wire coathangers into U-shaped pins, and pinning down branches so that they touch the dirt. If I'm feeling motivated, I scrape away a bit of bark on the underside, and dip that into rooting hormone.