For accurate advice, I think you have to give a better description of
what you have, starting with how deep your main lines are buried.

From what you have posted, it sounds like your main lines have risers,
with the heads screwed on top of the risers. Heads are generally about
six inches in height. Are yours sticking six inches up above the ground?

I would guess not, and that your risers are simply too long. You could
solve this by shortening the risers, but the better practice would be to
remove the risers, and fasten a supply line to the main line using an
elbow (this assembly would be well underground and not in danger of
being mowed). Then, using an elbow on the other end of the short supply
line (I like a two or three foot line to allow flex) attach the head to
the end of the short supply line and bury it appropriately, so the top
of the head is even with the surface of the ground. I like the
relatively long supply line, as over years the surface of your lawn may
rise (or fall, I suppose), and it is then relatively easy to reset the
sprinkler heads at the appropriate depth. Of course, pvc is not
appropriate in this situation as it is not at all flexible.

MiamiCuse wrote:
I am in zone 10 in Miami, FL and my sprinkler heads often get knocked out or
damaged by lawn mowers.

I got a few landscape guys to take a look and they proposed two methods to
solve it.

One proposed trenching deeper and reseating the sprinkler pipe deeper, and
thus burying the sprinkler head and let it be flushed with the ground level.
This means they have to trench six inches deeper for over 400 feet of pipes.

Second one proposed leaving the pipes where they are, but instead of
connecting the sprinker head to the threaded end on top of the pipe, to use
an elbow and funny pipe to bury a new sprinkler head 6 inches deep some
distance from the line.

The second method is much cheaper because not much digging is involved, but
I wonder if the lawn mower will knock off the elbow instead of the sprinker
heads?

Any comments? I really would like to get rid of those ugly concrete donuts
around each sprinkler head.

MC