Do I use risers or do I replace the heads with 4" ones? What are the pros and cons of each approach or is one of those appraches just plain dumb?
How high are you cutting the grass? If it's 2 1/2" to 3" then you will need to replace the heads with a 4" head. If the grass is being cut at less than 2", then your heads will work.
I've installed thousands of heads, and only one was a 2 1/2" head, and that one was because there was concrete under it, and I couldn't get a 4" head in that spot..
To get the heads at the proper height, you will have to dig them up and re-adjust them. Hopefully thay are already installed with swing joints and it'll only be a matter of re-positioning the swing joint and head to the proper height. The surface of the head, should be flush with the surface of the ground. The pop-up when extended, should reach up and over the turf.
www.sprinklerwarehouse.com/Hunter-Swing-Joints-s/6837.htm
If your heads were installed with risers with the tee fitting in the verticle position, I would remove the riser and install a swing joint with an extra fitting.
With a swing joint installed (properly), you should never have to replace a broken head again.
Mick