If you're really worried about getting your Zilla too hot, get an EGT.  By the time your water temp is skyrocketing, your top-end could already be toast.  An EGT won't prevent a meltdown either, but it will feed you a more accurate response 20x faster than the water temp will.

This is about as cheap as you can find, but you will need a power source.  http://www.ebay.com/itm/DIGITAL-EGT-THERMOMETER-PYROMETER-W-CLAMP-ON-PROBE-/200600832380?pt=Motors_Car_Truck_Parts_Accessories&vxp=mtr&hash=item2eb4bdc97c

About the best way to make sure you aren't overheating is to properly jet your bike with a plug chop and do a leakdown test.  Air leaks and wrong jetting are probably the biggest top-end killers out there.   

Yes an EGT will give you an approximate condition of your jetting.  The jetting affects water temperature very little.  Water temperature is primarily affected by the amount of power being produced and the air flow THROUGH the radiator. 

We have found that the major causes of high coolant temperatures are missing air scopes, after marker grills and corrosion inside the radiators.

If the engine is being worked hard in first and second gear the speeds are too low and the engine will usually overheat in a matter of a couple of minutes or less.   

Extra large radiators with air scopes may be required for low speed trail riding.  Cooling fans are not options for most two strokes because of their alternators low power output.