Yep, replacement as mentioned.
When you dig them up, don't be lazy, dig around them enough to prevent dirt falling back into the supply line below. If you don't keep dirt out, the new head will clog up the screens inside as soon as you turn the water back on.
Also, test the new heads before re-burying them. It is no fun having to dig them back up due to a leak or clogging due to dirt getting in the line.

ask me how I know.........