What kind of ground water?
Sounds like a dirty water situation that's damaging your sprinkler heads quicker.
Whats wrong with the heads? they stop rotating?
MOST k-rain are absolute crap, however a couple of the commercial krain's are kick ass.
Invest in a
in-series filter , Install a dedicated flush zone valve to help keep the system clean.
Over time as you are replacing your heads , if you really want a durable head. Start replacing them either with then
Rain Bird 5004 Stainless Steel , or the
Hunter I-20 Stainless steel
Depending on your system, you may need to invest in the next size up such as the Rain bird 5500's or the hunter i-25's